BMI calculator template

Free build guide: BMI calculator for WordPress

This guide rebuilds the BMI calculator from this site in Gravity Forms: 6 inputs, 6 live results and no submit button. Expect about 36 minutes by hand. The template above is the same form as an import file, and the bundle adds a PDF version of this guide with a screenshot of every setting, plus the stylesheet.

You will end up with:

• Your BMI
• Healthy weight from (lb)
• Healthy weight to (lb)
• Your BMI
• Healthy weight from (kg)
• Healthy weight to (kg)

What you need

• Gravity Forms (any license) — Calculation fields and conditional logic are in core.

Everything here is core Gravity Forms. No add-ons.

1. Create the form

1. Go to Forms → New Form and name it BMI.
2. In Form Settings → Form Layout, set the CSS Class Name to fo-live-only. Step 3 uses it to hide the submit button.
3. Leave the form open in the editor; the fields come next.

2. Add the fields, in this order

Field IDs are assigned as you add fields. If yours come out differently, change the {Label:ID} references in the formulas to match your IDs. Settings not mentioned stay at their defaults.

1. Units · Radio Buttons · ID 1
Custom CSS Class (Appearance tab) fo-segmented.

Choices (tick show values and enter each value):

• ft / lb — value us (selected by default)
• cm / kg — value metric

2. Height (ft) · Number · ID 2
Number Format 9,999.99; Default Value 5; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

3. Height (in) · Number · ID 3
Number Format 9,999.99; Default Value 9; Range min 0 max 11; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

4. Weight (lb) · Number · ID 4
Number Format 9,999.99; Default Value 160; Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

5. Your BMI · Number · ID 5
Number Format 9,999.99; Description “Under 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30+ obese”; Custom CSS Class (Appearance tab) fo-result; tick Enable Calculation, Rounding 1; Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

{Weight lb:4} * 703 / ( ( {Height ft:2} * 12 + {Height in:3} ) * ( {Height ft:2} * 12 + {Height in:3} ) )

6. Healthy weight from (lb) · Number · ID 6
Number Format 9,999.99; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0; Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

18.5 * ( {Height ft:2} * 12 + {Height in:3} ) * ( {Height ft:2} * 12 + {Height in:3} ) / 703

7. Healthy weight to (lb) · Number · ID 7
Number Format 9,999.99; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0; Conditional Logic (Advanced tab): Show this field if Units is ft / lb..

24.9 * ( {Height ft:2} * 12 + {Height in:3} ) * ( {Height ft:2} * 12 + {Height in:3} ) / 703

8. Height (cm) · Number · ID 8
Number Format 9,999.99; Default Value 175; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Conditional Logic (Advanced tab): Show this field if Units is cm / kg..

9. Weight (kg) · Number · ID 9
Number Format 9,999.99; Default Value 72; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Conditional Logic (Advanced tab): Show this field if Units is cm / kg..

10. Your BMI · Number · ID 10
Number Format 9,999.99; Description “Under 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30+ obese”; Custom CSS Class (Appearance tab) fo-result; tick Enable Calculation, Rounding 1; Conditional Logic (Advanced tab): Show this field if Units is cm / kg..

{Weight kg:9} * 10000 / ( {Height cm:8} * {Height cm:8} )

11. Healthy weight from (kg) · Number · ID 11
Number Format 9,999.99; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 1; Conditional Logic (Advanced tab): Show this field if Units is cm / kg..

18.5 * {Height cm:8} * {Height cm:8} / 10000

12. Healthy weight to (kg) · Number · ID 12
Number Format 9,999.99; Layout: half width, on the same row as its neighbour (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 1; Conditional Logic (Advanced tab): Show this field if Units is cm / kg..

24.9 * {Height cm:8} * {Height cm:8} / 10000

3. Hide the submit button

The results are live, so nothing needs submitting. Add this filter to your theme’s functions.php or a code-snippets plugin; it hides the button on any form carrying the fo-live-only class:

add_filter( 'gform_submit_button', function ( $button, $form ) {
	return str_contains( (string) rgar( $form, 'cssClass' ), 'fo-live-only' ) ? '' : $button;
}, 10, 2 );

Or with CSS alone: .fo-live-only_wrapper .gform_footer { display: none; }

4. Put it on a page and make it look like this

Add the form to any page with the Gravity Forms block, or the shortcode [gravityform id="X" title="false" ajax="false"]. The form inherits your theme’s styles; the classes you set in step 2 are hooks for the look you see on this site:

• fo-result on a calculation field makes it the big teal result panel.
• fo-result fo-result--sub makes the smaller secondary figures.
• fo-segmented on a radio field turns it into a segmented switch.
• Two fields on one row is the editor’s own column layout: drag a field beside another and the row splits in half. No CSS class is needed, and the old gf_left_half Ready Classes are deprecated.

The bundle includes the two stylesheets that implement those classes, with notes on matching your brand colours. Without them the form still works; it just looks like your theme’s default Gravity Forms styling.

How the maths works is explained under “How it’s calculated” on the live BMI calculator.