100% Free • No Sign-Up Required • Science-Backed

Free Fitness Calculators
Precise Results, Instantly

Calculate BMI, TDEE, body fat, macros, one-rep max, and more. All calculations run locally in your browser — your data stays private.

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All Calculators

Choose from 15 science-backed fitness calculators. Each uses established formulas from peer-reviewed research.

Body Composition

BMI Calculator

Calculate your Body Mass Index to assess whether your weight falls within a healthy range.

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Body Fat Calculator

Estimate your body-fat percentage using the U.S. Navy method with simple body measurements.

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Ideal Weight Calculator

Find your ideal body weight using multiple well-known medical formulas.

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Lean Body Mass Calculator

Estimate how much of your weight is muscle, bone, water, and organs versus fat.

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Waist-to-Hip Ratio Calculator

Measure your waist-to-hip ratio to assess central obesity and cardiovascular risk.

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Calories & Nutrition

BMR Calculator

Determine how many calories your body burns at complete rest with the Mifflin-St Jeor equation.

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TDEE Calculator

Estimate your Total Daily Energy Expenditure based on BMR and activity level.

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Calorie Deficit Calculator

Calculate how many calories to cut daily to reach your weight-loss goal safely.

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Macronutrient Calculator

Split your daily calories into optimal protein, carb, and fat targets for your goal.

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Water Intake Calculator

Determine how much water you should drink daily based on weight, activity, and climate.

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Strength & Performance

One Rep Max Calculator

Predict the maximum weight you can lift for a single repetition from your submaximal lifts.

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Wilks Score Calculator

Compare powerlifting performance across weight classes with the Wilks coefficient.

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Pace Calculator

Convert between pace, speed, and finish time for running and cycling events.

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Heart & Cardio

Heart Rate Zones Calculator

Calculate your five heart-rate training zones based on maximum or resting heart rate.

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VO2 Max Calculator

Estimate your maximal oxygen uptake, the gold-standard measure of cardiovascular fitness.

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Why Body Numbers?

Science-Backed

Every calculator uses peer-reviewed formulas from exercise science and nutrition research.

100% Private

All calculations happen in your browser. We never collect, store, or transmit your data.

Instant Results

No loading, no waiting. Get your results instantly with no account or sign-up required.

Frequently Asked Questions

Are these fitness calculators free to use?
Yes, all calculators on Body Numbers are completely free. There's no sign-up required, no hidden fees, and no limitations on usage. Use them as many times as you need.
How accurate are online fitness calculators?
Our calculators use scientifically validated formulas from peer-reviewed research. While they provide excellent estimates for most people, individual results may vary based on genetics, body composition, and medical conditions. They're best used as starting guidelines that you can adjust based on real-world results.
Is my data safe when using these calculators?
Absolutely. All calculations are performed entirely in your web browser using JavaScript. Your data never leaves your device — we don't collect, store, or transmit any of the information you enter into our calculators.
Which calculator should I start with?
If you're new to fitness tracking, start with the BMI Calculator for a quick health snapshot, then use the TDEE Calculator to find your daily calorie needs. From there, the Macro Calculator can help you plan your nutrition.
Do I need to create an account?
No. Body Numbers requires no account, no email, and no personal information. Just visit any calculator page and start using it immediately.
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