diff --git a/components/mjs/input/tex/extensions/fontsizev3/config.json b/components/mjs/input/tex/extensions/fontsizev3/config.json
new file mode 100644
index 000000000..9018bcc52
--- /dev/null
+++ b/components/mjs/input/tex/extensions/fontsizev3/config.json
@@ -0,0 +1,14 @@
+{
+  "build": {
+    "id": "[tex]/fontsizev3",
+    "component": "input/tex/extensions/fontsizev3",
+    "targets": ["input/tex/fontsizev3"]
+  },
+  "webpack": {
+    "name": "input/tex/extensions/fontsizev3",
+    "libs": [
+      "components/src/input/tex-base/lib",
+      "components/src/core/lib"
+    ]
+  }
+}
diff --git a/components/mjs/input/tex/extensions/fontsizev3/fontsizev3.js b/components/mjs/input/tex/extensions/fontsizev3/fontsizev3.js
new file mode 100644
index 000000000..df1c1e582
--- /dev/null
+++ b/components/mjs/input/tex/extensions/fontsizev3/fontsizev3.js
@@ -0,0 +1 @@
+import './lib/fontsizev3.js';
diff --git a/components/mjs/source.js b/components/mjs/source.js
index b6596c3c3..966413b69 100644
--- a/components/mjs/source.js
+++ b/components/mjs/source.js
@@ -49,6 +49,7 @@ export const source = {
   '[tex]/empheq': `${src}/input/tex/extensions/empheq/empheq.js`,
   '[tex]/enclose': `${src}/input/tex/extensions/enclose/enclose.js`,
   '[tex]/extpfeil': `${src}/input/tex/extensions/extpfeil/extpfeil.js`,
+  '[tex]/fontsizev3': `${src}/input/tex/extensions/fontsizev3/fontsizev3.js`,
   '[tex]/gensymb': `${src}/input/tex/extensions/gensymb/gensymb.js`,
   '[tex]/html': `${src}/input/tex/extensions/html/html.js`,
   '[tex]/mathtools': `${src}/input/tex/extensions/mathtools/mathtools.js`,
diff --git a/testsuite/tests/input/tex/__snapshots__/Base.test.ts.snap b/testsuite/tests/input/tex/__snapshots__/Base.test.ts.snap
index f884f9f5f..38f44cf04 100644
--- a/testsuite/tests/input/tex/__snapshots__/Base.test.ts.snap
+++ b/testsuite/tests/input/tex/__snapshots__/Base.test.ts.snap
@@ -7657,13 +7657,13 @@ exports[`Roots Tweaked Root 1`] = `
 
 exports[`Setting sizes Empty 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\Huge" display="block">
-  <mstyle mathsize="2.49em" data-latex="\\Huge"></mstyle>
+  <mstyle mathsize="2.074em" data-latex="\\Huge"></mstyle>
 </math>"
 `;
 
 exports[`Setting sizes Huge 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\Huge a" display="block">
-  <mstyle mathsize="2.49em" data-latex="\\Huge a">
+  <mstyle mathsize="2.074em" data-latex="\\Huge a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7671,7 +7671,7 @@ exports[`Setting sizes Huge 1`] = `
 
 exports[`Setting sizes LARGE 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\LARGE a" display="block">
-  <mstyle mathsize="1.73em" data-latex="\\LARGE a">
+  <mstyle mathsize="1.44em" data-latex="\\LARGE a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7679,7 +7679,7 @@ exports[`Setting sizes LARGE 1`] = `
 
 exports[`Setting sizes Large 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\Large a" display="block">
-  <mstyle mathsize="1.44em" data-latex="\\Large a">
+  <mstyle mathsize="1.2em" data-latex="\\Large a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7687,7 +7687,7 @@ exports[`Setting sizes Large 1`] = `
 
 exports[`Setting sizes Tiny 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\Tiny a" display="block">
-  <mstyle mathsize="0.6em" data-latex="\\Tiny a">
+  <mstyle mathsize="0.5em" data-latex="\\Tiny a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7695,7 +7695,7 @@ exports[`Setting sizes Tiny 1`] = `
 
 exports[`Setting sizes huge 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\huge a" display="block">
-  <mstyle mathsize="2.07em" data-latex="\\huge a">
+  <mstyle mathsize="1.728em" data-latex="\\huge a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7703,7 +7703,7 @@ exports[`Setting sizes huge 1`] = `
 
 exports[`Setting sizes large 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\large a" display="block">
-  <mstyle mathsize="1.2em" data-latex="\\large a">
+  <mstyle mathsize="1.095em" data-latex="\\large a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7727,7 +7727,7 @@ exports[`Setting sizes scriptsize 1`] = `
 
 exports[`Setting sizes small 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\small a" display="block">
-  <mstyle mathsize="0.85em" data-latex="\\small a">
+  <mstyle mathsize="0.9em" data-latex="\\small a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
@@ -7735,7 +7735,7 @@ exports[`Setting sizes small 1`] = `
 
 exports[`Setting sizes tiny 1`] = `
 "<math xmlns="http://www.w3.org/1998/Math/MathML" data-latex="\\tiny a" display="block">
-  <mstyle mathsize="0.5em" data-latex="\\tiny a">
+  <mstyle mathsize="0.6em" data-latex="\\tiny a">
     <mi data-latex="a">a</mi>
   </mstyle>
 </math>"
diff --git a/testsuite/tests/input/tex/__snapshots__/Mathtools.test.ts.snap b/testsuite/tests/input/tex/__snapshots__/Mathtools.test.ts.snap
index cd5d5956b..10111347d 100644
--- a/testsuite/tests/input/tex/__snapshots__/Mathtools.test.ts.snap
+++ b/testsuite/tests/input/tex/__snapshots__/Mathtools.test.ts.snap
@@ -3901,7 +3901,7 @@ exports[`Mathtools Symbols Other 1`] = `
   </mrow>
   <munder data-latex="\\mathop{\\Large\\kern-.1em\\boldsymbol{\\times}\\kern-.1em}_n">
     <mrow data-mjx-texclass="OP" data-latex="\\mathop{\\Large\\kern-.1em\\boldsymbol{\\times}\\kern-.1em}">
-      <mstyle mathsize="1.44em" data-latex="\\Large\\kern-.1em\\boldsymbol{\\times}\\kern-.1em">
+      <mstyle mathsize="1.2em" data-latex="\\Large\\kern-.1em\\boldsymbol{\\times}\\kern-.1em">
         <mspace width="-.1em" linebreak="nobreak" data-latex="\\kern-.1em"></mspace>
         <mo data-latex="\\boldsymbol{\\times}" mathvariant="bold">&#xD7;</mo>
         <mspace width="-.1em" linebreak="nobreak" data-latex="\\kern-.1em"></mspace>
diff --git a/ts/input/tex/base/BaseMappings.ts b/ts/input/tex/base/BaseMappings.ts
index e5bc0bb78..9ca684f77 100644
--- a/ts/input/tex/base/BaseMappings.ts
+++ b/ts/input/tex/base/BaseMappings.ts
@@ -452,16 +452,20 @@ new sm.CommandMap('macros', {
   textsf: [BaseMethods.HBox, null, VARIANT.SANSSERIF],
   texttt: [BaseMethods.HBox, null, VARIANT.MONOSPACE],
 
-  tiny: [BaseMethods.SetSize, 0.5],
-  Tiny: [BaseMethods.SetSize, 0.6], // non-standard
+  Tiny: [BaseMethods.SetSize, 0.5],
+  tiny: [BaseMethods.SetSize, 0.6],
   scriptsize: [BaseMethods.SetSize, 0.7],
-  small: [BaseMethods.SetSize, 0.85],
+  SMALL: [BaseMethods.SetSize, 0.7],
+  Small: [BaseMethods.SetSize, 0.8],
+  footnotesize: [BaseMethods.SetSize, 0.8],
+  small: [BaseMethods.SetSize, 0.9],
   normalsize: [BaseMethods.SetSize, 1.0],
-  large: [BaseMethods.SetSize, 1.2],
-  Large: [BaseMethods.SetSize, 1.44],
-  LARGE: [BaseMethods.SetSize, 1.73],
-  huge: [BaseMethods.SetSize, 2.07],
-  Huge: [BaseMethods.SetSize, 2.49],
+  large: [BaseMethods.SetSize, 1.095],
+  Large: [BaseMethods.SetSize, 1.2],
+  LARGE: [BaseMethods.SetSize, 1.44],
+  huge: [BaseMethods.SetSize, 1.728],
+  Huge: [BaseMethods.SetSize, 2.074],
+  HUGE: [BaseMethods.SetSize, 2.49],
 
   arcsin: BaseMethods.NamedFn,
   arccos: BaseMethods.NamedFn,
diff --git a/ts/input/tex/fontsizev3/FontSizeV3Configuration.ts b/ts/input/tex/fontsizev3/FontSizeV3Configuration.ts
new file mode 100644
index 000000000..969f54161
--- /dev/null
+++ b/ts/input/tex/fontsizev3/FontSizeV3Configuration.ts
@@ -0,0 +1,44 @@
+/*************************************************************
+ *
+ *  Copyright (c) 2026 The MathJax Consortium
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+/**
+ * @file Configuration file for the v3-compatible font size macros (\large, etc.)
+ *
+ * @author dpvc@mathjax.org (Davide P. Cervone)
+ */
+
+import { HandlerType, ConfigurationType } from '../HandlerTypes.js';
+import { CommandMap } from '../TokenMap.js';
+import { Configuration } from '../Configuration.js';
+import BaseMethods from '../base/BaseMethods.js';
+
+new CommandMap('fontsizev3-macros', {
+  tiny: [BaseMethods.SetSize, 0.5], //      // should have been .6
+  Tiny: [BaseMethods.SetSize, 0.6], //      // should have been .5
+  scriptsize: [BaseMethods.SetSize, 0.7],
+  small: [BaseMethods.SetSize, 0.85], //    // should have been .9
+  normalsize: [BaseMethods.SetSize, 1.0],
+  large: [BaseMethods.SetSize, 1.2], //     // should have been 1.095
+  Large: [BaseMethods.SetSize, 1.44], //    // should have been 1.2
+  LARGE: [BaseMethods.SetSize, 1.73], //    // should have been 1.44
+  huge: [BaseMethods.SetSize, 2.07], //     // should have been 1.728
+  Huge: [BaseMethods.SetSize, 2.49], //     // should have been 2.074
+});
+
+export const FontSizeV3Configuration = Configuration.create('fontsizev3', {
+  [ConfigurationType.HANDLER]: { [HandlerType.MACRO]: ['fontsizev3-macros'] },
+});