diff --git a/packages/propel/src/components/number-field/index.tsx b/packages/propel/src/components/number-field/index.tsx
index 7b6eeed9..a89d81ab 100644
--- a/packages/propel/src/components/number-field/index.tsx
+++ b/packages/propel/src/components/number-field/index.tsx
@@ -1,5 +1,7 @@
 export { NumberField, type NumberFieldProps } from "./number-field";
 export {
+  NumberFieldButtonIcon,
+  type NumberFieldButtonIconProps,
   NumberFieldDecrement,
   type NumberFieldDecrementProps,
   NumberFieldGroup,
@@ -8,4 +10,5 @@ export {
   type NumberFieldIncrementProps,
   NumberFieldInput,
   type NumberFieldInputProps,
+  type NumberFieldMagnitude,
 } from "../../ui/number-field";
diff --git a/packages/propel/src/components/number-field/number-field.stories.tsx b/packages/propel/src/components/number-field/number-field.stories.tsx
index 4dc55531..97ee5187 100644
--- a/packages/propel/src/components/number-field/number-field.stories.tsx
+++ b/packages/propel/src/components/number-field/number-field.stories.tsx
@@ -18,13 +18,13 @@ type Story = StoryObj<typeof meta>;
 
 /** A bounded numeric input with stepper buttons. */
 export const Default: Story = {
-  args: { defaultValue: 2, min: 1, max: 64 },
+  args: { defaultValue: 2, min: 1, max: 64, magnitude: "xl" },
 };
 
 /** Clicking the +/- buttons steps the value within `min`/`max`. */
 export const IncrementAndDecrement: Story = {
   tags: ["!dev", "!autodocs", "!manifest"],
-  args: { defaultValue: 2, min: 1, max: 64 },
+  args: { defaultValue: 2, min: 1, max: 64, magnitude: "xl" },
   play: async ({ canvas, userEvent }) => {
     const input = canvas.getByRole("textbox", { name: "Number of instances" });
     await expect(input).toHaveDisplayValue("2");
diff --git a/packages/propel/src/components/number-field/number-field.tsx b/packages/propel/src/components/number-field/number-field.tsx
index b063828b..bd24c07e 100644
--- a/packages/propel/src/components/number-field/number-field.tsx
+++ b/packages/propel/src/components/number-field/number-field.tsx
@@ -2,14 +2,19 @@ import { Minus, Plus } from "lucide-react";
 
 import {
   NumberField as NumberFieldRoot,
+  NumberFieldButtonIcon,
   NumberFieldDecrement,
   NumberFieldGroup,
   NumberFieldIncrement,
   NumberFieldInput,
+  type NumberFieldMagnitude,
   type NumberFieldProps as NumberFieldRootProps,
 } from "../../ui/number-field";
 
-export type NumberFieldProps = NumberFieldRootProps;
+export type NumberFieldProps = NumberFieldRootProps & {
+  /** Visual size of the field: controls button square and input height. Required. */
+  magnitude: NumberFieldMagnitude;
+};
 
 /**
  * The ready-made number field: a numeric input flanked by decrement / increment buttons. Drive it
@@ -23,18 +28,27 @@ export type NumberFieldProps = NumberFieldRootProps;
 export function NumberField({
   "aria-label": ariaLabel,
   "aria-labelledby": ariaLabelledby,
+  magnitude,
   ...props
 }: NumberFieldProps) {
   return (
     <NumberFieldRoot {...props}>
       <NumberFieldGroup>
-        <NumberFieldDecrement aria-label="Decrease">
-          <Minus aria-hidden className="size-4" />
+        <NumberFieldDecrement magnitude={magnitude} aria-label="Decrease">
+          <NumberFieldButtonIcon>
+            <Minus />
+          </NumberFieldButtonIcon>
         </NumberFieldDecrement>
         {/* The accessible name belongs on the input, not the root div. */}
-        <NumberFieldInput aria-label={ariaLabel} aria-labelledby={ariaLabelledby} />
-        <NumberFieldIncrement aria-label="Increase">
-          <Plus aria-hidden className="size-4" />
+        <NumberFieldInput
+          magnitude={magnitude}
+          aria-label={ariaLabel}
+          aria-labelledby={ariaLabelledby}
+        />
+        <NumberFieldIncrement magnitude={magnitude} aria-label="Increase">
+          <NumberFieldButtonIcon>
+            <Plus />
+          </NumberFieldButtonIcon>
         </NumberFieldIncrement>
       </NumberFieldGroup>
     </NumberFieldRoot>
diff --git a/packages/propel/src/ui/number-field/index.tsx b/packages/propel/src/ui/number-field/index.tsx
index 0b310f2c..8e4e9f25 100644
--- a/packages/propel/src/ui/number-field/index.tsx
+++ b/packages/propel/src/ui/number-field/index.tsx
@@ -1,5 +1,7 @@
 export { NumberField, type NumberFieldProps } from "./number-field";
+export { NumberFieldButtonIcon, type NumberFieldButtonIconProps } from "./number-field-button-icon";
 export { NumberFieldDecrement, type NumberFieldDecrementProps } from "./number-field-decrement";
 export { NumberFieldGroup, type NumberFieldGroupProps } from "./number-field-group";
 export { NumberFieldIncrement, type NumberFieldIncrementProps } from "./number-field-increment";
 export { NumberFieldInput, type NumberFieldInputProps } from "./number-field-input";
+export { type NumberFieldMagnitude } from "./variants";
diff --git a/packages/propel/src/ui/number-field/number-field-button-icon.tsx b/packages/propel/src/ui/number-field/number-field-button-icon.tsx
new file mode 100644
index 00000000..9f949a92
--- /dev/null
+++ b/packages/propel/src/ui/number-field/number-field-button-icon.tsx
@@ -0,0 +1,17 @@
+import type * as React from "react";
+
+import { numberFieldButtonIconVariants } from "./variants";
+
+export type NumberFieldButtonIconProps = Omit<
+  React.ComponentPropsWithoutRef<"span">,
+  "className" | "style"
+>;
+
+/**
+ * The icon slot inside a stepper button (`NumberFieldDecrement` or `NumberFieldIncrement`). Sizes
+ * its single child to the button's `--node-size` (set by the button's `magnitude`), so callers pass
+ * a bare icon with no size class. Decorative — the button carries the accessible name.
+ */
+export function NumberFieldButtonIcon(props: NumberFieldButtonIconProps) {
+  return <span aria-hidden className={numberFieldButtonIconVariants()} {...props} />;
+}
diff --git a/packages/propel/src/ui/number-field/number-field-decrement.tsx b/packages/propel/src/ui/number-field/number-field-decrement.tsx
index cf2d4ef8..952d773c 100644
--- a/packages/propel/src/ui/number-field/number-field-decrement.tsx
+++ b/packages/propel/src/ui/number-field/number-field-decrement.tsx
@@ -1,12 +1,20 @@
 import { NumberField as BaseNumberField } from "@base-ui/react/number-field";
 
-import { numberFieldButtonVariants } from "./variants";
+import { type NumberFieldMagnitude, numberFieldButtonVariants } from "./variants";
 
 export type NumberFieldDecrementProps = Omit<
   BaseNumberField.Decrement.Props,
   "className" | "style"
->;
+> & {
+  /**
+   * Visual size of the stepper button. Required — pick the magnitude that matches the field's
+   * density.
+   */
+  magnitude: NumberFieldMagnitude;
+};
 
-export function NumberFieldDecrement(props: NumberFieldDecrementProps) {
-  return <BaseNumberField.Decrement className={numberFieldButtonVariants()} {...props} />;
+export function NumberFieldDecrement({ magnitude, ...props }: NumberFieldDecrementProps) {
+  return (
+    <BaseNumberField.Decrement className={numberFieldButtonVariants({ magnitude })} {...props} />
+  );
 }
diff --git a/packages/propel/src/ui/number-field/number-field-increment.tsx b/packages/propel/src/ui/number-field/number-field-increment.tsx
index f659f4c4..8fd10bc1 100644
--- a/packages/propel/src/ui/number-field/number-field-increment.tsx
+++ b/packages/propel/src/ui/number-field/number-field-increment.tsx
@@ -1,12 +1,20 @@
 import { NumberField as BaseNumberField } from "@base-ui/react/number-field";
 
-import { numberFieldButtonVariants } from "./variants";
+import { type NumberFieldMagnitude, numberFieldButtonVariants } from "./variants";
 
 export type NumberFieldIncrementProps = Omit<
   BaseNumberField.Increment.Props,
   "className" | "style"
->;
+> & {
+  /**
+   * Visual size of the stepper button. Required — pick the magnitude that matches the field's
+   * density.
+   */
+  magnitude: NumberFieldMagnitude;
+};
 
-export function NumberFieldIncrement(props: NumberFieldIncrementProps) {
-  return <BaseNumberField.Increment className={numberFieldButtonVariants()} {...props} />;
+export function NumberFieldIncrement({ magnitude, ...props }: NumberFieldIncrementProps) {
+  return (
+    <BaseNumberField.Increment className={numberFieldButtonVariants({ magnitude })} {...props} />
+  );
 }
diff --git a/packages/propel/src/ui/number-field/number-field-input.tsx b/packages/propel/src/ui/number-field/number-field-input.tsx
index 38ee8698..29965b35 100644
--- a/packages/propel/src/ui/number-field/number-field-input.tsx
+++ b/packages/propel/src/ui/number-field/number-field-input.tsx
@@ -1,9 +1,12 @@
 import { NumberField as BaseNumberField } from "@base-ui/react/number-field";
 
-import { numberFieldInputVariants } from "./variants";
+import { type NumberFieldMagnitude, numberFieldInputVariants } from "./variants";
 
-export type NumberFieldInputProps = Omit<BaseNumberField.Input.Props, "className" | "style">;
+export type NumberFieldInputProps = Omit<BaseNumberField.Input.Props, "className" | "style"> & {
+  /** Visual size of the input. Required — must match the stepper buttons' magnitude. */
+  magnitude: NumberFieldMagnitude;
+};
 
-export function NumberFieldInput(props: NumberFieldInputProps) {
-  return <BaseNumberField.Input className={numberFieldInputVariants()} {...props} />;
+export function NumberFieldInput({ magnitude, ...props }: NumberFieldInputProps) {
+  return <BaseNumberField.Input className={numberFieldInputVariants({ magnitude })} {...props} />;
 }
diff --git a/packages/propel/src/ui/number-field/number-field.stories.tsx b/packages/propel/src/ui/number-field/number-field.stories.tsx
index 7341ea9d..fc0190a5 100644
--- a/packages/propel/src/ui/number-field/number-field.stories.tsx
+++ b/packages/propel/src/ui/number-field/number-field.stories.tsx
@@ -4,6 +4,7 @@ import { expect } from "storybook/test";
 
 import {
   NumberField,
+  NumberFieldButtonIcon,
   NumberFieldDecrement,
   NumberFieldGroup,
   NumberFieldIncrement,
@@ -16,7 +17,13 @@ import {
 const meta = {
   title: "UI/NumberField",
   component: NumberField,
-  subcomponents: { NumberFieldGroup, NumberFieldInput, NumberFieldDecrement, NumberFieldIncrement },
+  subcomponents: {
+    NumberFieldGroup,
+    NumberFieldInput,
+    NumberFieldButtonIcon,
+    NumberFieldDecrement,
+    NumberFieldIncrement,
+  },
 } satisfies Meta<typeof NumberField>;
 
 export default meta;
@@ -28,12 +35,16 @@ export const Default: Story = {
   render: (args) => (
     <NumberField {...args} aria-label="Number of instances">
       <NumberFieldGroup>
-        <NumberFieldDecrement aria-label="Decrease instances">
-          <Minus aria-hidden className="size-4" />
+        <NumberFieldDecrement magnitude="xl" aria-label="Decrease instances">
+          <NumberFieldButtonIcon>
+            <Minus />
+          </NumberFieldButtonIcon>
         </NumberFieldDecrement>
-        <NumberFieldInput aria-label="Number of instances" />
-        <NumberFieldIncrement aria-label="Increase instances">
-          <Plus aria-hidden className="size-4" />
+        <NumberFieldInput magnitude="xl" aria-label="Number of instances" />
+        <NumberFieldIncrement magnitude="xl" aria-label="Increase instances">
+          <NumberFieldButtonIcon>
+            <Plus />
+          </NumberFieldButtonIcon>
         </NumberFieldIncrement>
       </NumberFieldGroup>
     </NumberField>
@@ -47,12 +58,16 @@ export const IncrementAndDecrement: Story = {
   render: (args) => (
     <NumberField {...args} aria-label="Number of instances">
       <NumberFieldGroup>
-        <NumberFieldDecrement aria-label="Decrease instances">
-          <Minus aria-hidden className="size-4" />
+        <NumberFieldDecrement magnitude="xl" aria-label="Decrease instances">
+          <NumberFieldButtonIcon>
+            <Minus />
+          </NumberFieldButtonIcon>
         </NumberFieldDecrement>
-        <NumberFieldInput aria-label="Number of instances" />
-        <NumberFieldIncrement aria-label="Increase instances">
-          <Plus aria-hidden className="size-4" />
+        <NumberFieldInput magnitude="xl" aria-label="Number of instances" />
+        <NumberFieldIncrement magnitude="xl" aria-label="Increase instances">
+          <NumberFieldButtonIcon>
+            <Plus />
+          </NumberFieldButtonIcon>
         </NumberFieldIncrement>
       </NumberFieldGroup>
     </NumberField>
diff --git a/packages/propel/src/ui/number-field/variants.ts b/packages/propel/src/ui/number-field/variants.ts
index 376376eb..d9057bcf 100644
--- a/packages/propel/src/ui/number-field/variants.ts
+++ b/packages/propel/src/ui/number-field/variants.ts
@@ -1,4 +1,6 @@
-import { cva, cx } from "class-variance-authority";
+import { type VariantProps, cva, cx } from "class-variance-authority";
+
+import { nodeSlotClass } from "../../internal/node-slot";
 
 export const numberFieldRootVariants = cva("flex min-w-0 flex-col gap-1.5");
 export const numberFieldGroupVariants = cva(
@@ -8,13 +10,50 @@ export const numberFieldGroupVariants = cva(
     "data-disabled:cursor-not-allowed data-disabled:border-subtle data-disabled:bg-layer-2",
   ),
 );
+
+// Button geometry per magnitude. Each magnitude sets a square size and a `--node-size`
+// CSS variable that the `NumberFieldButtonIcon` node-slot reads to size the child icon.
+// Figma S/Base/L/XL map to sm/md/lg/xl (20/24/28/32 px). The icon runs one step
+// smaller than the button (14/16/16/20 px) matching the icon-button glyph scale.
 export const numberFieldButtonVariants = cva(
   cx(
-    "flex size-8 items-center justify-center text-icon-secondary transition-colors outline-none",
+    "flex shrink-0 items-center justify-center text-icon-secondary transition-colors outline-none",
     "hover:bg-layer-transparent-hover focus-visible:bg-layer-transparent-hover",
     "data-disabled:cursor-not-allowed data-disabled:text-disabled",
   ),
+  {
+    variants: {
+      magnitude: {
+        sm: "size-5 [--node-size:0.875rem]", // 20 px box, 14 px glyph
+        md: "size-6 [--node-size:1rem]", // 24 px box, 16 px glyph
+        lg: "size-7 [--node-size:1rem]", // 28 px box, 16 px glyph
+        xl: "size-8 [--node-size:1.25rem]", // 32 px box, 20 px glyph
+      },
+    },
+  },
 );
+
+// The icon slot inside a stepper button. Sizes its single child to the button's
+// `--node-size` (inherited from the button element above), so callers pass a bare icon.
+export const numberFieldButtonIconVariants = cva(nodeSlotClass);
+
+// Shared magnitude type so all parts stay in sync.
+export type NumberFieldMagnitude = NonNullable<
+  VariantProps<typeof numberFieldButtonVariants>["magnitude"]
+>;
+
+// Input geometry per magnitude. Heights match the button square per magnitude so the
+// group container stays flush. The width is fixed to accommodate up to ~4 digits.
 export const numberFieldInputVariants = cva(
-  "h-8 w-16 bg-transparent text-center text-14 text-primary outline-none disabled:text-disabled",
+  "w-14 bg-transparent text-center text-14 text-primary outline-none disabled:text-disabled",
+  {
+    variants: {
+      magnitude: {
+        sm: "h-5",
+        md: "h-6",
+        lg: "h-7",
+        xl: "h-8",
+      },
+    },
+  },
 );