Use the Calculation Feature on your WordPress Form for Free with Ninja Forms

Did you know? You can use the calculation feature on your WordPress form—for free!

The free Ninja Forms core plugin (download), can perform a wide range of calculations—whether it’s multiplying (*), dividing (/), adding (+), subtracting(-), or power of (^) —all directly within your forms.

This Calculation feature offers exceptional versatility, serving a wide range of purposes. You can total product orders, apply discounts, calculate age from birth year, score leads and quizzes, and much more. By automating these calculations, accuracy and efficiency are significantly improved, while also enhancing the overall user experience.

Table of Contents

1. Fields you can use in calculations
2. Create PPI calculator WordPress form
3. Create Mortgage calculator WordPress form
4. Create BMI calculator WordPress form

List of the fields that you can use in calculations:

• Single Checkbox: Allow users to select a single item.
• Checkbox List : Enable users to choose one or more items.
• Select: Let users select a single item from a dropdown menu.
• Multi-Select: Permit users to choose multiple items from a dropdown menu.
• Radio List: Allow users to select a single item from a list.
• Select Image: Enable users to choose one or more items by selecting images.
• Number: Let users enter a numerical value.
• Hidden field: Enables you to assign a default value and keep it concealed from users.

How to create a Pixel Density(PPI) Calculator WordPress form

You can easily create a form that allows users to calculate the Pixel Density (PPI) of their screens at no cost. Users will simply need to provide the following screen details:

• Width in pixels
• Height in pixels
• Diagonal size in inches

1. Start by installing the free Ninja Forms core plugin (download) on your WordPress site.
2. Create a new form that includes fields for Name, Email, three Number fields (for the three measurements), and an HTML field to display the Pixel Density (PPI).
3. Go to the Advanced tab and select Calculations, where you’ll input the PPI formula: {√(Width² + Height²)}/Diagonal.
4. Divide the formula into three manageable variables:
   1. Width² + Height²—name this “Add_squares.”
   2. √(Width² + Height²)—name this “Squareroot.”
   3. {√(Width² + Height²)}/Diagonal—name this “PPI.”

5. Use the Merge Tag icon to select the fields or calculations you want to use. Insert the necessary operations (+, -, /, *, ^) for each of the three variables. Save your formulas by clicking Done.

How to create a Mortgage Calculator WordPress form for free

Yes, you can create a Mortgage Calculator form using Ninja Forms without spending a dime. Users simply need to provide the following details: Mortgage Debt(Principal), Term (Years), and Mortgage Interest Rate. Once these are entered into the form, the monthly payments will be calculated automatically.

To get started, install the free Ninja Forms core plugin(download) on your WordPress site and create a form with 3 Number fields, 1 Hidden field, and 1 HTML field.

1. Name the three Number fields: Principal, Term (Years), and Yearly Interest Rate.  The Field Keys as p,t, and r respectively. Name the Hidden field as “Number of Payments per Year.” and its Field key as n.
2. In the Advanced tab, click Calculations to add the following formula for monthly payments = P[R/N] / [1 – (1 + R/N)^(-NT)]

1. • Break the formula into two parts for easier understanding.
   • Name the first part (P[R/N]) as “calc1,” and the second part ([1 – (1 + R/N)^(-NT)]) as “calc2.” Then, divide calc1 by calc2 to get the result, naming it “calc3.”

3. Set the HTML field to display the calculated result by setting its default value to “Monthly Mortgage Payment” and using the merge tag “calc3.”
4. Save the formulas by clicking Done.

How to create a BMI Calculator WordPress form for free

 You can create a WordPress form that calculates BMI using different measurement systems. Let’s focus on two methods:

• Kilograms/meters, the formula is weight (kg) / height² (meters).
• Pounds/inches, the formula is weight (lbs) / [height (in)]² × 703.

1. Start by installing the free Ninja Forms core plugin (downloadable), and create a form with four Number fields and two HTML fields.
2. Label the Number fields as follows: Weight (kg), Height (meters), Weight (lbs), and Height (inches).
3. To set up the BMI calculations, go to the Advanced tab, select Calculations, and add new variables for the four formulas: calc1, bmi1, calc2, and bmi2.
4. Use the Merge Tags feature to select the fields or calculations you want to reference, and insert the necessary math symbols by simply typing them.

5. Set the HTML fields to display the BMI calculations.

Enhance the user experience

You can enhance the user experience by allowing form users to choose their preferred measurement system, such as Kg/M or lbs/inches. You can implement this with a Radio Button field and the Conditional Logic add-on. At Ninja Forms, we offer single add-on purchases unlike our competitors.

You only pay for the individual add-on; in this case, you only pay for the Conditional Logic add-on. Alternatively, if you are looking for multiple add-ons, take advantage of our hugely discounted Membership plans.

Radio Button field settings

Conditional Logic add-on settings

This is where the conditional logic is set to display BMI in kg/m. Now, create similar second part of the logic to display BMI in lbs/in.

Ninja Forms’ free & powerful calculation feature will maximize savings for you!

The writing is on the wall: with Ninja Forms, you can create WordPress forms with advanced calculations—completely free. Whether you need an Order Form, Insurance Calculator Form, Return on Investment Calculator Form, or Saving and Investment Calculator Form, we’ve got you covered. And with our Layout & Styles add-on, you can effortlessly transform your forms into beautifully designed, professional-looking layouts.

At Ninja Forms, we’ve taken a different approach by offering our core plugin at no cost. It comes loaded with essential features to kickstart your form-building journey. Our goal is to ensure you don’t have to wait until you’re generating revenue to access a premium product.

And it gets even better! Whether you’re using our free core plugin, an add-on, or a membership, you’ll always receive top-tier support.

Blog articles are provided as a courtesy to show you all the cool things you can do with Ninja Forms.  However, troubleshooting complex calculation setups and mathematical order of operations are outside the scope of support we are able to provide. If you find a reproducible bug, however, please let us know!