Body Fat Calculator

📖 Tool Introduction

The Body Fat Calculator uses the US Navy circumference method, a technique widely adopted in fitness circles to estimate what percentage of your weight is made up of fat. Compared with body weight or BMI alone, body fat paints a much truer picture of leanness: two people of the same weight can look completely different because one carries far more muscle than the other. The tool applies two separate empirical formulas depending on your sex — men need height, waist and neck measurements, while women also include the hip. At the top, two cards let you pick male or female; choosing female smoothly reveals the hip field, while choosing male hides it again so the form stays uncluttered. Simply measure yourself relaxed with a soft tape in centimetres, and the tool converts everything to inches and feeds the numbers into the logarithmic formula behind the scenes. The result area shows your body fat percentage in a large, friendly figure, and a coloured badge below it rates the value as low, athletic, fit, acceptable or high, with a short reference line explaining the typical healthy ranges. Every calculation runs locally in your browser, so none of your measurements are ever uploaded. The interface ships in Simplified Chinese, Traditional Chinese and English, and adapts to both phone and desktop screens for a comfortable measurement session at home. Because it depends only on a tape measure rather than expensive equipment, it is an easy companion to revisit whenever your training or diet enters a new phase: record the figure after a few weeks of consistent exercise, or compare two measurements taken under the same conditions to see whether the fat is actually moving, rather than guessing from the scale alone. Used this way, the estimate stops being a single snapshot and becomes a small, honest dashboard of body composition trends that you can check any time, anywhere, with complete peace of mind about privacy.

✨ Key Features

• US Navy method: two empirical formulas, one per sex, for a reasoned estimate of fat percentage
• Gender-aware form: the hip field appears for women and hides itself for men
• Automatic unit conversion: measure in centimetres and the tool handles inches internally
• Health rating: a colour badge classifies the result as low, athletic, fit, acceptable or high
• Big readable number: the body fat percentage is shown prominently at a glance
• One-click copy: the percentage and rating can be copied to track progress over time

📝 How to Use

1. Pick your sex on the cards at the top
2. Enter height, waist and neck; add your hip measurement if you are female
3. Measure waist at belly-button level and neck below the larynx, relaxed
4. Click Calculate to see the large percentage and its coloured rating badge
5. Click Copy result to record it, or click Example to try a sample

⚠️ Notes

• An estimate: the circumference method is empirical and less precise than calipers or a BIA scale
• Technique matters: tape tension and breathing affect the reading, so measure a few times and average
• Reasonable data: a man's waist must exceed his neck; odd values trigger a friendly warning
• Rough bands: healthy ranges vary by age and sex, so the badge is only a broad guide
• Privacy: all math runs in the browser and no body measurements leave your device