diff --git a/js/Dimension3.ts b/js/Dimension3.ts
new file mode 100644
index 0000000..76ca48f
--- /dev/null
+++ b/js/Dimension3.ts
@@ -0,0 +1,140 @@
+// Copyright 2013-2023, University of Colorado Boulder
+
+/**
+ * Dimension3 is a basic width, height, and depth, like a Bounds3 but without the position defined.
+ *
+ * @author Jonathan Olson <jonathan.olson@colorado.edu>
+ * @author Chris Malley (PixelZoom, Inc.)
+ */
+
+import dot from './dot.js';
+import InfiniteNumberIO from '../../tandem/js/types/InfiniteNumberIO.js';
+import { StateObject } from '../../tandem/js/types/StateSchema.js';
+import IOType from '../../tandem/js/types/IOType.js';
+import Bounds3 from './Bounds3.js';
+
+const STATE_SCHEMA = {
+  width: InfiniteNumberIO,
+  height: InfiniteNumberIO,
+  depth: InfiniteNumberIO
+};
+export type Dimension3StateObject = StateObject<typeof STATE_SCHEMA>;
+
+export default class Dimension3 {
+
+  public width: number;
+  public height: number;
+  public depth: number;
+
+  public constructor( width: number, height: number, depth: number ) {
+    this.width = width;
+    this.height = height;
+    this.depth = depth;
+  }
+
+  /**
+   * Debugging string for the dimension.
+   */
+  public toString(): string {
+    return `[${this.width}w, ${this.height}h, ${this.depth}d]`;
+  }
+
+  /**
+   * Sets this dimension to be a copy of another dimension.
+   * This is the mutable form of the function copy(). This will mutate (change) this dimension, in addition to returning
+   * this dimension itself.
+   */
+  public set( dimension: Dimension3 ): Dimension3 {
+    this.width = dimension.width;
+    this.height = dimension.height;
+    this.depth = dimension.depth;
+    return this;
+  }
+
+  /**
+   * Sets the width of the dimension, returning this.
+   */
+  public setWidth( width: number ): Dimension3 {
+    this.width = width;
+    return this;
+  }
+
+  /**
+   * Sets the height of the dimension, returning this.
+   */
+  public setHeight( height: number ): Dimension3 {
+    this.height = height;
+    return this;
+  }
+
+  /**
+   * Sets the depth of the dimension, returning this.
+   */
+  public setDepth( depth: number ): Dimension3 {
+    this.depth = depth;
+    return this;
+  }
+
+  /**
+   * Creates a copy of this dimension, or if a dimension is passed in, set that dimension's values to ours.
+   * This is the immutable form of the function set(), if a dimension is provided. This will return a new dimension,
+   * and will not modify this dimension.
+   *
+   * @param [dimension] - If not provided, creates a new Dimension3 with filled in values. Otherwise, fills
+   *                      in the values of the provided dimension so that it equals this dimension.
+   */
+  public copy( dimension?: Dimension3 ): Dimension3 {
+    if ( dimension ) {
+      return dimension.set( this );
+    }
+    else {
+      return new Dimension3( this.width, this.height, this.depth );
+    }
+  }
+
+  /**
+   * Creates a Bounds2 from this dimension based on passing in the minimum (top-left) corner as (x,y).
+   * @param [x] - Minimum x coordinate of the bounds, or 0 if not provided.
+   * @param [y] - Minimum y coordinate of the bounds, or 0 if not provided.
+   * @param [z] - Minimum z coordinate of the bounds, or 0 if not provided.
+   */
+  public toBounds( x?: number, y?: number, z?: number ): Bounds3 {
+    x = x !== undefined ? x : 0;
+    y = y !== undefined ? y : 0;
+    z = z !== undefined ? z : 0;
+    return new Bounds3( x, y, z, this.width + x, this.height + y, this.depth + z );
+  }
+
+  /**
+   * Exact equality comparison between this dimension and another dimension.
+   */
+  public equals( that: Dimension3 ): boolean {
+    return this.width === that.width && this.height === that.height && this.depth === that.depth;
+  }
+
+  public toStateObject(): Dimension3StateObject {
+    return {
+      width: InfiniteNumberIO.toStateObject( this.width ),
+      height: InfiniteNumberIO.toStateObject( this.height ),
+      depth: InfiniteNumberIO.toStateObject( this.depth )
+    };
+  }
+
+  public static fromStateObject( stateObject: Dimension3StateObject ): Dimension3 {
+    return new Dimension3(
+      InfiniteNumberIO.fromStateObject( stateObject.width ),
+      InfiniteNumberIO.fromStateObject( stateObject.height ),
+      InfiniteNumberIO.fromStateObject( stateObject.depth )
+    );
+  }
+
+  public static Dimension3IO = new IOType<Dimension3, Dimension3StateObject>( 'Dimension3IO', {
+    valueType: Dimension3,
+    documentation: 'A dimension with "width", "height", and "depth" members.',
+    stateSchema: STATE_SCHEMA,
+    toStateObject: ( range: Dimension3 ) => range.toStateObject(),
+    fromStateObject: ( stateObject: Dimension3StateObject ) => Dimension3.fromStateObject( stateObject )
+  } );
+}
+
+dot.register( 'Dimension3', Dimension3 );
\ No newline at end of file