diff --git a/js/common/view/ThermometerAndReadout.ts b/js/common/view/ThermometerAndReadout.ts
index 1e1d76c5..620e4985 100644
--- a/js/common/view/ThermometerAndReadout.ts
+++ b/js/common/view/ThermometerAndReadout.ts
@@ -151,6 +151,14 @@ class ThermometerAndReadout extends Node {
         tandem: options.tandem.createTandem( 'comboBox' )
       } );
       this.addChild( comboBox );
+
+      // Make sure the NumberDisplays are all the same width, https://github.com/phetsims/greenhouse-effect/issues/256
+      const maxItemWidth = Math.max( ..._.map( comboBox.nodes, 'width' ) );
+      comboBox.nodes.forEach( ( node: Node ) => {
+        if ( node instanceof NumberDisplay ) {
+          node.setBackgroundWidth( maxItemWidth );
+        }
+      } );
     }
     else {
 
@@ -212,14 +220,6 @@ class ThermometerAndReadout extends Node {
                                      propertyValue: TemperatureUnits,
                                      tandemName: string ): ComboBoxItem<TemperatureUnits> {
 
-    // Set a minimum background width for the number display.  This is necessary because the nodes that go into the
-    // combo box must be the same size, or things can look weird, see
-    // https://github.com/phetsims/greenhouse-effect/issues/256.  The approach of using a hard-coded constant is
-    // admittedly quite brittle, but because of the constraints of ComboBox, it's hard to figure out the sizes of the
-    // displays before creating them.  So, hard coded it is.  Be wary if reusing this.  The value was empirically
-    // determined.
-    const minNumberDisplayBackgroundWidth = 68;
-
     const numberDisplayOptions = {
       backgroundStroke: null,
       decimalPlaces: DECIMAL_PLACES_IN_READOUT,
@@ -228,15 +228,14 @@ class ThermometerAndReadout extends Node {
         maxWidth: 120
       },
       valuePattern: new PatternStringProperty(
-        GreenhouseEffectStrings.temperature.units.valueUnitsPatternStringProperty,
-        { units: unitsStringProperty }
-      ),
-      minBackgroundWidth: minNumberDisplayBackgroundWidth
+        GreenhouseEffectStrings.temperature.units.valueUnitsPatternStringProperty, {
+          units: unitsStringProperty
+        } )
     };
 
     return {
       value: propertyValue,
-      createNode: tandem => new NumberDisplay( property, propertyRange, numberDisplayOptions ),
+      createNode: () => new NumberDisplay( property, propertyRange, numberDisplayOptions ),
       tandemName: tandemName,
       a11yName: TemperatureDescriber.getTemperatureUnitsString( propertyValue )
     };