How to Measure
Accurate measurements are essential for a reliable estimate. Use a flexible tape measure (fabric or plastic, not metal) and follow these guidelines:
Neck
Measure just below the larynx (Adam's apple). Keep the tape level — don't angle it downward at the front. Record to the nearest 0.5 cm.
Waist
Men: Measure at navel (belly button) level. Stand relaxed — don't suck in your stomach.
Women: Measure at the narrowest point of your natural waist, typically between the bottom of your ribs and the top of your hip bones.
Hip (Women Only)
Measure at the widest point of your hips and buttocks. Keep the tape level all the way round.
The US Navy Method
This calculator uses the US Navy circumference method, developed by Hodgdon and Beckett in 1984. It's one of the most widely validated field methods for estimating body fat and is still used by military organisations worldwide.
The Formulae
Men:
%BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women:
%BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
All measurements in centimetres. The calculator handles imperial-to-metric conversion automatically.
How Accurate Is It?
Research shows the Navy method typically estimates body fat within ±3–4% of DEXA scan results for most people. It's less accurate at the extremes — very lean individuals (<10% BF) and those with very high body fat (>35%) may see larger deviations.
Body Fat Categories
Body fat percentage norms differ between men and women due to essential fat requirements (women carry more essential fat for reproductive function).
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25–31% | 32–39% |
| Obese | 32%+ | 40%+ |
What's a Good Body Fat Percentage?
For general health, most experts recommend:
- Men: 10–20% body fat
- Women: 18–28% body fat
Going below essential fat levels is dangerous and can cause hormonal disruption, immune suppression, and organ damage. There's no need to aim for athlete-level leanness unless you're actively competing.
Body Fat vs BMI
BMI and body fat percentage measure different things:
- BMI uses only height and weight — it can't distinguish between muscle and fat. A muscular person may have a high BMI but healthy body fat.
- Body fat percentage directly estimates how much of your weight is fat tissue. It's a more meaningful measure of health risk.
For a complete picture, use both together. Our BMI calculator complements this tool well.
How to Reduce Body Fat
Diet
- A moderate calorie deficit (300–500 kcal/day) promotes fat loss while preserving muscle
- Prioritise protein (1.6–2.2g per kg bodyweight) to maintain muscle mass
- Eat mostly whole foods — vegetables, lean proteins, whole grains, healthy fats
- Avoid crash diets — rapid weight loss often means losing muscle, not just fat
Exercise
- Resistance training (weights, bodyweight exercises) is the most effective way to preserve and build muscle while losing fat
- Cardio helps create a calorie deficit but shouldn't be your only strategy
- Aim for 150+ minutes of moderate activity per week (NHS recommendation)
- HIIT (high-intensity interval training) can be time-efficient for fat loss
When to See a Professional
- Body fat over 32% (men) or 40% (women)
- Difficulty losing fat despite consistent effort
- Considering very low body fat for competition — work with a sports dietitian
- History of disordered eating — seek support before pursuing fat loss
More Calcify Calculators
- BMI Calculator UK — Body Mass Index with NHS categories
- UK Mortgage Calculator — Repayment, interest-only & stamp duty
- UK Salary & Tax Calculator — 2025/26 PAYE, NI, student loans
- Compound Interest Calculator — Savings growth & ISA projections
- All Calculators →