FitnessCalculator

Free Health & Fitness Calculators

Check your BMI, daily calorie needs, body fat percentage, ideal weight and water intake in seconds. Choose kilograms or pounds, centimetres or feet, on any tool. The tools calculate on your device and do not send your measurements to our server.

BMI Calculator

Body Mass Index. A quick screen for whether your weight sits in a healthy range for your height.
kg
cm
–
–
Healthy weight range
–

BMI calculator page: the formula, the chart and what the categories mean

Calorie / TDEE Calculator

Estimate the calories you burn daily and how much to eat to lose, maintain or gain weight.
kg
cm
–
BMR (at rest)
–
Mild weight loss
–
Maintain
–
Mild weight gain
–

Calorie and TDEE calculator page: how BMR, activity and deficits fit together

Body Fat Calculator

Estimate body fat percentage using the U.S. Navy tape method.
cm
cm
in
cm
in
–
–

Body fat calculator page: how to measure, and the percentage charts by age and sex

Ideal Weight Calculator

A healthy target-weight range for your height, based on established medical formulas.
cm
–
Devine formula
–
Robinson formula
–
BMI-based range
–

Ideal weight calculator page: where the formulas came from and what to use instead

Water Intake Calculator

How much water to drink per day based on your weight and exercise.
kg
–
In cups (240 ml)
–
In fluid ounces
–

Water intake calculator page: daily targets by weight, and where the eight-glass rule came from

Each calculator on its own page

The same tool, with the formula written out, the reference charts and the questions people actually ask about it.

BMI Calculator for Adults Calculate adult BMI in kg/cm or pounds/feet. See your position on the BMI scale, screening category… Calorie and TDEE Calculator Estimate maintenance calories with Mifflin–St Jeor. Compare activity levels and calorie scenarios, follow the calculation steps,… Navy Body Fat Calculator Estimate body fat with the traditional Navy tape method. Use the measurement diagram, see your calculation… Ideal Weight Calculator Compare Devine, Robinson, Miller and Hamwi estimates with an adult BMI-based range. Use cm or feet,… Water Intake Calculator by Weight Estimate water intake by weight and exercise. Separate food and drinks, enter your bottle size in…

Read the guides

What each formula is doing, where it was derived, and the situations where it gives the wrong answer.

BMI scale showing the underweight, healthy, overweight and obese bands with cutoffs marked at 18.5, 25 and 30 What BMI Actually Measures, and Where It Falls Apart Learn how adult BMI is calculated, where its categories come from, and why it cannot diagnose health or distinguish muscle from fat. Bar chart comparing a 1,780 kcal resting BMR against a 2,759 kcal TDEE, with the 979 kcal activity gap bracketed BMR vs TDEE: Which Number Should You Actually Eat To? Understand estimated resting energy, daily expenditure and calorie scenarios without treating BMR as a personal minimum intake. How Big Should a Calorie Deficit Be? Compare calorie-deficit examples and learn why fixed calorie rules cannot promise a weekly weight-loss result. Picking an Activity Multiplier Without Fooling Yourself See how activity multipliers change TDEE, why step counts are only context, and how to avoid counting exercise twice. The Navy Body Fat Method: How to Measure It and How Wrong It Can Be Measure for the traditional Navy circumference equations, understand their units, and avoid treating body-fat estimates as a diagnosis. Why Ideal Weight Formulas Disagree With Each Other Compare Devine, Robinson, Miller and Hamwi formulas, including their different outputs and why none defines a personal ideal weight. How Much Water You Actually Need Per Day Understand total water from food and drinks, the assumptions in the water calculator, and why there is no universal bottle target. Why the Scale Jumps Two Kilos Overnight Learn how water, food and measurement conditions affect scale weight, and when an unexplained change needs medical advice. How Big Should a Calorie Surplus Be? Compare small calorie-surplus scenarios and understand why extra food cannot predict a specific amount of muscle gain. How Much Protein You Actually Need Per Day Put protein research ranges in context, calculate an example intake, and understand why study averages are not personal prescriptions. Why Your Calorie Count Is Wrong, and by How Much Understand serving sizes, food logs and watch estimates without assuming a fixed error percentage applies to your calorie count. Why Weight Loss Stalls, and What to Change First Review a weight-loss plateau without automatically cutting calories, blaming tracking or assuming metabolism is permanently damaged.
About these calculators

BMI is body weight in kilograms divided by height in metres squared. Daily calories use the Mifflin-St Jeor equation for resting metabolism, multiplied by an activity factor to give total daily energy expenditure (TDEE). Body fat uses the U.S. Navy circumference method. Ideal weight shows the Devine and Robinson formulas alongside the healthy-BMI range. Water intake is estimated from body weight plus an allowance for exercise. These are general estimates for healthy adults and do not replace medical advice.