Body Fat Calculator

What Is a Body Fat Calculator?

BMI tells you whether your weight is proportionate to your height. Body fat percentage tells you what that weight is actually made of. Two people can have identical BMIs but very different body compositions — a muscular athlete and a sedentary person of the same height and weight can look completely different and carry completely different health risks.

Healthy body fat ranges vary by sex and age. For adult men, 10–20% is generally considered healthy (athletes often sit at 6–13%). For adult women, 18–28% is typical for good health (athletes 14–20%). Above these ranges, risk of type 2 diabetes, heart disease, and joint problems increases. Below them — particularly below 5% for men and 12% for women — carries its own health risks.

This calculator uses the US Navy method: a reliable formula based on height, neck circumference, and waist (and hip for women). Measure at the widest point for waist, the narrowest for neck. The result is approximate — DEXA scanning is the gold standard — but accurate enough to be useful.

How Do You Use This Body Fat Calculator?

Enter your gender, height, waist circumference, neck circumference, and hip circumference (women only) to estimate your body fat percentage using the US Navy method.

1. Select your gender (male or female), as the formula differs for each.
2. Enter your height in centimetres or feet and inches.
3. Measure your waist circumference at the narrowest point (navel level for men) and enter the value.
4. Measure your neck circumference just below the larynx and enter the value.
5. If female, measure your hip circumference at the widest point and enter the value.
6. Click calculate to see your estimated body fat percentage and fitness classification.

How Does the Body Fat Calculator Formula Work?

The formula used: Body Fat % (men) = 495 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height)) - 450; Body Fat % (women) = 495 / (1.29579 - 0.35004 * log10(waist + hip - neck) + 0.22100 * log10(height)) - 450

What Are Some Example Calculations?

A male with a waist of 85 cm, neck of 38 cm, and height of 178 cm: Body Fat % = 495 / (1.0324 - 0.19077 * log10(85 - 38) + 0.15456 * log10(178)) - 450 = approximately 17.7%.

When Should You Use a Body Fat Calculator?

When tracking a body recomposition programme — building muscle while losing fat. Your weight might stay flat or increase while your body fat percentage drops, which is why relying on scales alone can be misleading and demoralising. Measure monthly and track both numbers.

When BMI has flagged you as overweight but you suspect it's muscle, not fat. A trained weightlifter with a BMI of 28 might have 15% body fat — well within the healthy range. Body fat percentage is the more meaningful metric in that situation, and this calculator gives you a quick estimate without needing a lab.

What Do These Terms Mean?

What Are the Best Tips to Know?

• Take measurements first thing in the morning before eating or drinking for the most consistent results.
• Use a flexible tape measure and keep it snug but not compressing the skin.
• Measure each site two or three times and use the average to reduce error.
• Track your measurements over weeks rather than days, as daily fluctuations are normal.
• Combine body fat estimates with other metrics like waist-to-hip ratio for a fuller health picture.

What Mistakes Should You Avoid?

• Measuring the waist at the belt line instead of the narrowest point (or navel level for men), which inflates the result.
• Pulling the tape measure too tight or leaving it too loose, both of which distort circumference readings.
• Comparing results from different methods (e.g., US Navy vs. bioelectrical impedance) as though they are interchangeable.
• Expecting day-to-day precision from an estimation method — use trends over time rather than single readings.