diff --git a/lib/flutter_auto_size_text.dart b/lib/flutter_auto_size_text.dart
index bf429ce..591e4e8 100644
--- a/lib/flutter_auto_size_text.dart
+++ b/lib/flutter_auto_size_text.dart
@@ -1 +1,22 @@
-export 'src/auto_size_text.dart';
+library;
+
+import 'dart:async';
+import 'dart:math';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+part 'src/auto_size_group.dart';
+
+part 'src/auto_size_group_builder.dart';
+
+part 'src/auto_size_text.dart';
+
+part 'src/text_fitter.dart';
+
+part 'src/auto_size_builder/auto_size.dart';
+
+part 'src/auto_size_builder/auto_size_builder.dart';
+
+part 'src/auto_size_builder/auto_size_element.dart';
+
+part 'src/auto_size_builder/render_auto_size.dart';
diff --git a/lib/src/auto_size_builder/auto_size.dart b/lib/src/auto_size_builder/auto_size.dart
index 08cd144..6273e5b 100644
--- a/lib/src/auto_size_builder/auto_size.dart
+++ b/lib/src/auto_size_builder/auto_size.dart
@@ -1,4 +1,4 @@
-part of 'auto_size_builder.dart';
+part of '../../flutter_auto_size_text.dart';
 
 class _AutoSize extends RenderObjectWidget {
   _AutoSize({
@@ -17,13 +17,15 @@ class _AutoSize extends RenderObjectWidget {
     required this.textScaleFactor,
     required this.minFontSize,
     required this.maxFontSize,
+    this.groupMaxFontSize,
     required this.stepGranularity,
     required this.presetFontSizes,
+    this.onMaxPossibleFontSizeChanged,
   }) {
     _validateProperties();
   }
 
-  final AutoSizeTextBuilder builder;
+  final _AutoSizeTextBuilder builder;
   final Widget? overflowReplacement;
 
   final TextSpan text;
@@ -41,6 +43,8 @@ class _AutoSize extends RenderObjectWidget {
   final double maxFontSize;
   final double stepGranularity;
   final List<double>? presetFontSizes;
+  final double? groupMaxFontSize;
+  final void Function(double)? onMaxPossibleFontSizeChanged;
 
   TextFitter _buildFitter() {
     return TextFitter(
@@ -64,13 +68,17 @@ class _AutoSize extends RenderObjectWidget {
 
   @override
   _RenderAutoSize createRenderObject(BuildContext context) {
-    return _RenderAutoSize(fitter: _buildFitter());
+    return _RenderAutoSize(
+        fitter: _buildFitter(),
+        onMaxPossibleFontSizeChanged: onMaxPossibleFontSizeChanged,
+        groupMaxFontSize: groupMaxFontSize);
   }
 
   @override
   void updateRenderObject(
       BuildContext context, covariant _RenderAutoSize renderObject) {
     renderObject.updateTextFitter(_buildFitter());
+    renderObject.updateGroupMaxFontSize(groupMaxFontSize);
   }
 
   @override
diff --git a/lib/src/auto_size_builder/auto_size_builder.dart b/lib/src/auto_size_builder/auto_size_builder.dart
index 6ccdf56..eb605ee 100644
--- a/lib/src/auto_size_builder/auto_size_builder.dart
+++ b/lib/src/auto_size_builder/auto_size_builder.dart
@@ -1,16 +1,10 @@
-import 'package:flutter/rendering.dart';
-import 'package:flutter/widgets.dart';
-import 'package:flutter_auto_size_text/src/text_fitter.dart';
+part of '../../flutter_auto_size_text.dart';
 
-part 'auto_size.dart';
-part 'auto_size_element.dart';
-part 'render_auto_size.dart';
+typedef _AutoSizeTextBuilder = Widget Function(BuildContext context,
+    double textScaleFactor, double? groupMaxFontSize, bool overflow);
 
-typedef AutoSizeTextBuilder = Widget Function(
-    BuildContext context, double textScaleFactor, bool overflow);
-
-class AutoSizeBuilder extends StatefulWidget {
-  const AutoSizeBuilder({
+class _AutoSizeBuilder extends StatefulWidget {
+  const _AutoSizeBuilder({
     super.key,
     required this.builder,
     this.overflowReplacement,
@@ -30,9 +24,10 @@ class AutoSizeBuilder extends StatefulWidget {
     this.maxFontSize,
     this.stepGranularity,
     this.presetFontSizes,
+    this.group,
   });
 
-  final AutoSizeTextBuilder builder;
+  final _AutoSizeTextBuilder builder;
 
   /// {@macro auto_size_text.overflowReplacement}
   final Widget? overflowReplacement;
@@ -83,11 +78,29 @@ class AutoSizeBuilder extends StatefulWidget {
   /// {@macro auto_size_text.presetFontSizes}
   final List<double>? presetFontSizes;
 
+  /// {@macro auto_size_text.group}
+  final AutoSizeGroup? group;
+
   @override
-  State<AutoSizeBuilder> createState() => _AutoSizeBuilderState();
+  State<_AutoSizeBuilder> createState() => _AutoSizeBuilderState();
 }
 
-class _AutoSizeBuilderState extends State<AutoSizeBuilder> {
+class _AutoSizeBuilderState extends State<_AutoSizeBuilder> {
+  @override
+  void initState() {
+    super.initState();
+    widget.group?._register(this);
+  }
+
+  @override
+  void didUpdateWidget(covariant _AutoSizeBuilder oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.group != widget.group) {
+      oldWidget.group?._remove(this);
+      widget.group?._register(this);
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final defaultTextStyle = DefaultTextStyle.of(context);
@@ -127,8 +140,24 @@ class _AutoSizeBuilderState extends State<AutoSizeBuilder> {
       textScaleFactor: widget.textScaleFactor ?? 1,
       minFontSize: widget.minFontSize ?? 12.0,
       maxFontSize: widget.maxFontSize ?? double.infinity,
+      groupMaxFontSize: widget.group?._effectiveMaxPossibleFontSize,
       stepGranularity: widget.stepGranularity ?? 1.0,
       presetFontSizes: widget.presetFontSizes,
+      onMaxPossibleFontSizeChanged: widget.group != null
+          ? (maxPossibleFontSize) {
+              widget.group?._updateFontSize(this, maxPossibleFontSize);
+            }
+          : null,
     );
   }
+
+  void _notifySync() {
+    setState(() {});
+  }
+
+  @override
+  void dispose() {
+    widget.group?._remove(this);
+    super.dispose();
+  }
 }
diff --git a/lib/src/auto_size_builder/auto_size_element.dart b/lib/src/auto_size_builder/auto_size_element.dart
index e5e9868..e7b9145 100644
--- a/lib/src/auto_size_builder/auto_size_element.dart
+++ b/lib/src/auto_size_builder/auto_size_element.dart
@@ -1,4 +1,4 @@
-part of 'auto_size_builder.dart';
+part of '../../flutter_auto_size_text.dart';
 
 class _AutoSizeElement extends RenderObjectElement {
   _AutoSizeElement(_AutoSize super.widget);
@@ -40,12 +40,12 @@ class _AutoSizeElement extends RenderObjectElement {
     super.unmount();
   }
 
-  void _updateText(double textScaleFactor, bool overflow) {
+  void _updateText(double textScaleFactor, double? groupMaxFontSize, bool overflow) {
     owner!.buildScope(this, () {
       _overflow = overflow;
       Widget built;
       try {
-        built = widget.builder(this, textScaleFactor, overflow);
+        built = widget.builder(this, textScaleFactor, groupMaxFontSize, overflow);
         debugWidgetBuilderValue(widget, built);
       } catch (e) {
         built = ErrorWidget(e);
diff --git a/lib/src/auto_size_builder/render_auto_size.dart b/lib/src/auto_size_builder/render_auto_size.dart
index 6c72190..1f6f087 100644
--- a/lib/src/auto_size_builder/render_auto_size.dart
+++ b/lib/src/auto_size_builder/render_auto_size.dart
@@ -1,4 +1,4 @@
-part of 'auto_size_builder.dart';
+part of '../../flutter_auto_size_text.dart';
 
 class _AutoSizeParentData extends ParentData
     with ContainerParentDataMixin<RenderBox> {}
@@ -7,7 +7,11 @@ class _RenderAutoSize extends RenderBox
     with
         ContainerRenderObjectMixin<RenderBox,
             ContainerParentDataMixin<RenderBox>> {
-  _RenderAutoSize({required TextFitter fitter}) : _fitter = fitter;
+  _RenderAutoSize(
+      {required TextFitter fitter,
+      this.onMaxPossibleFontSizeChanged,
+      required this.groupMaxFontSize})
+      : _fitter = fitter;
 
   var _overflow = false;
   var _needsBuild = true;
@@ -15,8 +19,11 @@ class _RenderAutoSize extends RenderBox
   bool? _previousOverflow;
   double? _longestWordWidth;
 
-  Function(double, bool)? _buildCallback;
-  void updateBuildCallback(Function(double, bool)? buildCallback) {
+  Function(double, double?, bool)? _buildCallback;
+  double? groupMaxFontSize;
+  final void Function(double)? onMaxPossibleFontSizeChanged;
+
+  void updateBuildCallback(Function(double, double?, bool)? buildCallback) {
     if (_buildCallback == buildCallback) return;
     _previousTextScaleFactor = null;
     _buildCallback = buildCallback;
@@ -24,6 +31,7 @@ class _RenderAutoSize extends RenderBox
   }
 
   TextFitter _fitter;
+
   void updateTextFitter(TextFitter fitter) {
     if (_fitter == fitter) return;
     if (_fitter.text != fitter.text) {
@@ -34,6 +42,12 @@ class _RenderAutoSize extends RenderBox
     markNeedsLayout();
   }
 
+  void updateGroupMaxFontSize(double? newGroupMaxFontSize) {
+    if (groupMaxFontSize == newGroupMaxFontSize) return;
+    groupMaxFontSize = newGroupMaxFontSize;
+    markNeedsLayout();
+  }
+
   RenderBox get child => _overflow ? lastChild! : firstChild!;
 
   bool get hasReplacement => !identical(firstChild, lastChild);
@@ -115,8 +129,11 @@ class _RenderAutoSize extends RenderBox
       _previousTextScaleFactor = result.scale;
       _previousOverflow = result.overflow;
       _needsBuild = false;
-      invokeLayoutCallback(
-          (_) => _buildCallback!(result.scale, result.overflow));
+      final fontSize = _fitter.text.style?.fontSize ?? _kDefaultFontSize;
+      final maxPossibleFontSize = fontSize * result.scale;
+      onMaxPossibleFontSizeChanged?.call(maxPossibleFontSize);
+      invokeLayoutCallback((_) =>
+          _buildCallback!(result.scale, groupMaxFontSize, result.overflow));
     }
 
     _overflow = result.overflow;
diff --git a/lib/src/auto_size_group.dart b/lib/src/auto_size_group.dart
new file mode 100644
index 0000000..8f286c8
--- /dev/null
+++ b/lib/src/auto_size_group.dart
@@ -0,0 +1,49 @@
+part of '../flutter_auto_size_text.dart';
+
+/// Controller to synchronize the fontSize of multiple AutoSizeTexts.
+class AutoSizeGroup {
+  final _listeners = <_AutoSizeBuilderState, double>{};
+  var _widgetsNotified = false;
+
+  void _register(_AutoSizeBuilderState text) {
+    _listeners[text] = double.infinity;
+  }
+
+  double get _effectiveMaxPossibleFontSize {
+    final minMaxPossibleFontSize = _listeners.values.fold<double>(
+        double.infinity,
+        (previousValue, element) =>
+            element < previousValue ? element : previousValue);
+    return minMaxPossibleFontSize;
+  }
+
+  void _updateFontSize(_AutoSizeBuilderState text, double maxPossibleFontSize) {
+    final oldEffectiveMaxPossibleFontSize = _effectiveMaxPossibleFontSize;
+    _listeners[text] = maxPossibleFontSize;
+    final newEffectiveMaxPossibleFontSize = _effectiveMaxPossibleFontSize;
+
+    if (oldEffectiveMaxPossibleFontSize != newEffectiveMaxPossibleFontSize) {
+      _widgetsNotified = false;
+      scheduleMicrotask(_notifyListeners);
+    }
+  }
+
+  void _notifyListeners() {
+    if (_widgetsNotified) {
+      return;
+    } else {
+      _widgetsNotified = true;
+    }
+
+    for (final textState in _listeners.keys) {
+      if (textState.mounted) {
+        textState._notifySync();
+      }
+    }
+  }
+
+  void _remove(_AutoSizeBuilderState text) {
+    _updateFontSize(text, double.infinity);
+    _listeners.remove(text);
+  }
+}
diff --git a/lib/src/auto_size_group_builder.dart b/lib/src/auto_size_group_builder.dart
new file mode 100644
index 0000000..49d274a
--- /dev/null
+++ b/lib/src/auto_size_group_builder.dart
@@ -0,0 +1,22 @@
+part of '../flutter_auto_size_text.dart';
+
+/// A Flutter widget that provides an [AutoSizeGroup] to its builder function.
+class AutoSizeGroupBuilder extends StatefulWidget {
+  final Widget Function(BuildContext context, AutoSizeGroup autoSizeGroup)
+      builder;
+
+  /// Creates an [AutoSizeGroupBuilder] widget.
+  const AutoSizeGroupBuilder({super.key, required this.builder});
+
+  @override
+  _AutoSizeGroupBuilderState createState() => _AutoSizeGroupBuilderState();
+}
+
+class _AutoSizeGroupBuilderState extends State<AutoSizeGroupBuilder> {
+  final _group = AutoSizeGroup();
+
+  @override
+  Widget build(BuildContext context) {
+    return widget.builder(context, _group);
+  }
+}
diff --git a/lib/src/auto_size_text.dart b/lib/src/auto_size_text.dart
index f98263e..de3443b 100644
--- a/lib/src/auto_size_text.dart
+++ b/lib/src/auto_size_text.dart
@@ -1,5 +1,4 @@
-import 'package:flutter/widgets.dart';
-import 'package:flutter_auto_size_text/src/auto_size_builder/auto_size_builder.dart';
+part of '../flutter_auto_size_text.dart';
 
 /// Flutter widget that automatically resizes text to fit perfectly within its
 /// bounds.
@@ -140,7 +139,7 @@ class AutoSizeText extends StatelessWidget {
   /// If you want multiple [AutoSizeText]s to have the same text size, give all
   /// of them the same [AutoSizeGroup] instance. All of them will have the
   /// size of the smallest [AutoSizeText]
-  //final AutoSizeGroup? group;
+  final AutoSizeGroup? group;
 
   /// {@template auto_size_text.wrapWords}
   /// Whether words which don't fit in one line should be wrapped.
@@ -185,11 +184,11 @@ class AutoSizeText extends StatelessWidget {
     this.maxFontSize,
     this.stepGranularity,
     this.presetFontSizes,
-    //this.group,
+    this.group,
     this.wrapWords,
     this.overflowReplacement,
     this.overflowCallback,
-  })  : textSpan = null;
+  }) : textSpan = null;
 
   /// Creates a [AutoSizeText] widget with a [TextSpan].
   const AutoSizeText.rich(
@@ -212,20 +211,27 @@ class AutoSizeText extends StatelessWidget {
     this.maxFontSize,
     this.stepGranularity,
     this.presetFontSizes,
-    //this.group,
+    this.group,
     this.wrapWords,
     this.overflowReplacement,
     this.overflowCallback,
-  })  : data = null;
+  }) : data = null;
 
   @override
   Widget build(BuildContext context) {
     final span = textSpan ?? TextSpan(text: data);
-    return AutoSizeBuilder(
+    return _AutoSizeBuilder(
       text: span,
       style: style,
-      builder: (context, scale, overflow) {
+      builder: (context, scale, groupMaxFontSize, overflow) {
         overflowCallback?.call(overflow);
+        final fontSize =
+            span.style?.fontSize ?? style?.fontSize ?? _kDefaultFontSize;
+        final scaledFontSize = fontSize * scale;
+        final adjustedScale =
+            groupMaxFontSize != null && scaledFontSize > groupMaxFontSize
+                ? groupMaxFontSize / fontSize
+                : scale;
         return Text.rich(
           span,
           key: textKey,
@@ -236,7 +242,7 @@ class AutoSizeText extends StatelessWidget {
           locale: locale,
           softWrap: softWrap,
           overflow: this.overflow,
-          textScaler: TextScaler.linear(scale),
+          textScaler: TextScaler.linear(adjustedScale),
           maxLines: maxLines,
           semanticsLabel: semanticsLabel,
         );
@@ -246,6 +252,7 @@ class AutoSizeText extends StatelessWidget {
       maxFontSize: maxFontSize,
       stepGranularity: stepGranularity,
       presetFontSizes: presetFontSizes,
+      group: group,
       textAlign: textAlign,
       textDirection: textDirection,
       locale: locale,
diff --git a/lib/src/text_fitter.dart b/lib/src/text_fitter.dart
index 31339df..878e0ac 100644
--- a/lib/src/text_fitter.dart
+++ b/lib/src/text_fitter.dart
@@ -1,6 +1,4 @@
-import 'dart:math';
-
-import 'package:flutter/widgets.dart';
+part of '../flutter_auto_size_text.dart';
 
 const _kDefaultFontSize = 14;
 
diff --git a/test/group_builder_test.dart b/test/group_builder_test.dart
new file mode 100644
index 0000000..b391438
--- /dev/null
+++ b/test/group_builder_test.dart
@@ -0,0 +1,103 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_auto_size_text/flutter_auto_size_text.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'utils.dart';
+
+Widget testWidget({required double width1, required double width2}) {
+  return MaterialApp(
+    home: AutoSizeGroupBuilder(
+      builder: (_, group) => Column(
+        children: <Widget>[
+          SizedBox(
+            width: width1,
+            height: 100,
+            child: AutoSizeText(
+              'XXXXXX',
+              style: const TextStyle(fontSize: 60),
+              minFontSize: 1,
+              maxLines: 1,
+              group: group,
+            ),
+          ),
+          SizedBox(
+            width: width2,
+            height: 100.0,
+            child: AutoSizeText(
+              'XXXXXX',
+              style: const TextStyle(fontSize: 60),
+              minFontSize: 1,
+              maxLines: 1,
+              group: group,
+            ),
+          ),
+        ],
+      ),
+    ),
+  );
+}
+
+void _expectFontSizes(WidgetTester tester, double fontSize) {
+  final texts = tester.widgetList(find.byType(RichText));
+  for (final text in texts) {
+    expect(effectiveFontSize(text as RichText), fontSize);
+  }
+}
+
+void main() {
+  testWidgets('Group sync', (tester) async {
+    await tester.pumpWidget(testWidget(width1: 300, width2: 300));
+
+    _expectFontSizes(tester, 50);
+
+    await tester.pumpWidget(testWidget(width1: 200, width2: 300));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 33);
+
+    await tester.pumpWidget(testWidget(width1: 200, width2: 150));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 25);
+
+    await tester.pumpWidget(testWidget(width1: 200, width2: 100));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 16);
+
+    await tester.pumpWidget(testWidget(width1: 60, width2: 60));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 10);
+
+    await tester.pumpWidget(testWidget(width1: 200, width2: 60));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 10);
+
+    await tester.pumpWidget(testWidget(width1: 200, width2: 250));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 33);
+
+    await tester.pumpWidget(testWidget(width1: 250, width2: 250));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+
+    _expectFontSizes(tester, 41);
+
+    await tester.pumpWidget(testWidget(width1: 300, width2: 300));
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    // Upsizing both requires an extra frame to settle on the new size.
+    await tester.pump();
+
+    _expectFontSizes(tester, 50);
+  });
+}
diff --git a/test/group_test.dart b/test/group_test.dart
new file mode 100644
index 0000000..0a158ea
--- /dev/null
+++ b/test/group_test.dart
@@ -0,0 +1,121 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_auto_size_text/flutter_auto_size_text.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'utils.dart';
+
+class GroupTest extends StatefulWidget {
+  @override
+  GroupTestState createState() => GroupTestState();
+}
+
+class GroupTestState extends State<GroupTest> {
+  AutoSizeGroup group = AutoSizeGroup();
+  double width1 = 300.0;
+  double width2 = 300.0;
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Column(
+        children: <Widget>[
+          SizedBox(
+            width: width1,
+            height: 100,
+            child: AutoSizeText(
+              'XXXXXX',
+              style: const TextStyle(fontSize: 60),
+              minFontSize: 1,
+              maxLines: 1,
+              group: group,
+            ),
+          ),
+          SizedBox(
+            width: width2,
+            height: 100.0,
+            child: AutoSizeText(
+              'XXXXXX',
+              style: const TextStyle(fontSize: 60),
+              minFontSize: 1,
+              maxLines: 1,
+              group: group,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+
+  void refresh() {
+    setState(() {});
+  }
+}
+
+void _expectFontSizes(WidgetTester tester, double fontSize) {
+  final texts = tester.widgetList(find.byType(RichText));
+  for (final text in texts) {
+    expect(effectiveFontSize(text as RichText), fontSize);
+  }
+}
+
+void main() {
+  testWidgets('Group sync', (tester) async {
+    await tester.pumpWidget(GroupTest());
+
+    _expectFontSizes(tester, 50);
+
+    final state = tester.state(find.byType(GroupTest)) as GroupTestState;
+
+    state.width1 = 200;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 33);
+
+    state.width2 = 150;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 25);
+
+    state.width2 = 100;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 16);
+
+    state.width1 = 60;
+    state.width2 = 60;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 10);
+
+    state.width1 = 200;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 10);
+
+    state.width2 = 250;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 33);
+
+    state.width1 = 250;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 41);
+
+    state.width1 = 300;
+    state.width2 = 300;
+    state.refresh();
+    await tester.pump(Duration.zero);
+    await tester.pump(Duration.zero);
+    _expectFontSizes(tester, 50);
+
+    await tester.pump(Duration.zero);
+  });
+}