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    Body Fat Calculator

    🇳🇿 New Zealand version

    In New Zealand, body measurements are normally taken in centimetres and kilograms, and this body fat calculator starts there. The US Navy equation takes neck, waist and height, with hips for women, and the page labels the percentage with a category and an age range. Use it as a rough guide and ask your GP how to read it.

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    Use Body Fat Calculator online

    Body Fat Calculator

    Calculate your body fat percentage using the US Navy method

    Personal Information

    Body Measurements (cm)

    New Zealand rules and figures

    • The New Zealand page begins on Metric, so weight is kilograms and height, neck, waist and hip are centimetres.
    • In the Ministry of Health adult guideline, Healthy weight is 18.5 to 24.9 and Obesity is a single band from 30, so the BMI here is not split into classes.
    • Neither the Ministry nor Health NZ publishes lower numbers for Asian ethnicities, though both mention that waist thresholds or the healthy BMI may sit lower.
    • Adult bands do not apply to children and young people, who have separate Ministry of Health clinical guidelines.

    Sources: Ministry of Health: Weight management in adults (2017) (checked 2026-11-08); Health NZ: Healthy weight BMI calculator (checked 2026-11-08); Ministry of Health: Weight management in children and young people (checked 2026-11-08)

    How the body fat calculator works

    The calculator takes base-10 logarithms of tape readings in centimetres, applies the equation for the chosen sex and subtracts 450 from the scaled result.

    body fat % = 495 ÷ (a − b × log10(c) + d × log10(height)) − 450, where c is waist − neck for men and waist + hip − neck for women

    • Metric is the starting Unit System, so weight is kilograms and every length is in centimetres. Pick Imperial and the labels turn to pounds and inches.
    • Women see age ranges of 14-21% under 30, 15-23% in their 30s, 16-25% in their 40s and 17-27% from 50, shown beside the percentage.
    • Nothing is saved between visits, and a page reload clears every box.
    • A blank age shows the prompt "Enter age" instead of a range, and the percentage and category are unaffected.

    How to use the body fat calculator

    1. Choose gender and units. Pick Male or Female. Keep Unit System on Metric unless your tape is marked in inches.
    2. Add age and body size. Type your age, then weight in kilograms and height in centimetres.
    3. Take three measurements. Measure the neck below the larynx, the waist, and for women the hips at their widest point.
    4. Compare with the tables. Open Categories to see the bands for each sex, or Guide for tape placement tips.
    5. Copy the summary. Copy Results gives plain text containing the percentage, category, BMI and your measurements.

    Example: 175 cm at age 52, 160 cm at age 36

    A man who is 52, 175 cm and 90 kg with a 40 cm neck and 92 cm waist comes out at 20.7%, Average, inside a 16-22% range, with a BMI of 29.4. A woman who is 36, 160 cm and 58 kg with a 31 cm neck, 76 cm waist and 96 cm hip comes out at 30.3%, Average, in a 15-23% range, BMI 22.7.

    When to use the body fat calculator

    • Checking waist-driven change. Re-enter the same neck and height with a new waist to see how much the percentage moves.
    • Putting a BMI in context. Use the percentage beside the BMI to see whether a heavier build looks muscular or not on paper.
    • Planning a conversation with your GP. Print or copy the result so the visit starts from the same numbers.

    What the body fat calculator does not do

    • A tape-based estimate cannot see muscle mass, bone density or where fat is stored.
    • The categories and age ranges are built into the page and are not from the Ministry of Health or Health NZ.
    • No New Zealand body fat threshold for Asian ethnicities is available from the sources checked, so none is applied.
    • The estimate stays in the page only until you reload it, unless you copy it.

    When something else is a better fit

    • When you want your tape readings saved with dates, use the Body Measurement Tracker, which stores dated entries.
    • When you want a weight band from the Ministry of Health categories, use the BMI Calculator.
    • When you want advice on what the numbers mean for you, use your GP, who may also suggest a waist measurement or other checks.

    Questions about the body fat calculator

    Why do I get no percentage?

    The equation needs a positive value for waist minus neck, or waist plus hip minus neck. When it is not, the page shows a message. Re-take the tape readings in centimetres and keep the tape level.

    Does the percentage depend on my age?

    No. Age only selects the range text, and a blank age shows "Enter age". A man of 52 sees 16-22% whatever percentage the equation returns.

    Are these categories official in New Zealand?

    No. They are the calculator's own bands, the same in every country. The Ministry of Health and Health NZ publish BMI guidance, not body fat categories.

    Can I use pounds and inches?

    Yes, switch Unit System to Imperial and enter pounds and inches. The page then converts to centimetres and kilograms, using 2.54 and 0.45359237, before running the equation.