Lean: Body Fat & BMI

A calm, cited body-composition calculator: body fat %, lean mass, BMI, BMR and TDEE from published formulas. No account, and your numbers never leave your device.

Most body-fat apps are loud, ad-stuffed, and built on guesswork. Lean is the opposite — a calm, cited calculator that respects your time and your data.

What Lean calculates • Body fat % using the U.S. Navy circumference method (Hodgdon & Beckett, 1984) • Lean body mass and fat mass in lb or kg • BMI with the standard category (Underweight → Obese) • BMR (resting calories) via the Mifflin–St Jeor equation • TDEE (daily calorie burn) with five activity multipliers • Healthy body-fat range and goal weight at the midpoint of that range • Animated band strip with a live tick that updates as you type

Why Lean is more trustworthy than the rest We don't make up numbers. Every formula in this app comes from a published source you can verify in the "How this is calculated" sheet — one tap from the Calculator tab.

• U.S. Navy circumference method — Naval Health Research Center, Hodgdon & Beckett (1984), refined by NHRC technical reports. Estimates body fat within ±3–4% of a DEXA scan for most adults. • Mifflin–St Jeor BMR equation — Mifflin et al., American Journal of Clinical Nutrition, 1990. The most accurate general-population BMR formula. • Healthy body-fat ranges — American Council on Exercise (ACE), general-adult percent body-fat norms by sex.

Male and female formulas Lean uses the correct circumference inputs for each sex. Male: neck + waist + height. Female: neck + waist + hips + height. The healthy range, body-fat band thresholds, and goal weight all adjust automatically.

Metric or imperial Switch between cm/kg and in/lb at any time. Every input converts on the fly. Set it once in More → Units and never see the wrong system again.

Your progress, without an account Tap the bookmark on the Calculator tab and Lean saves a snapshot of every meaningful number: body fat %, lean mass, fat mass, BMI, weight, and date. The Progress tab shows the delta since your last save and the trend since you started. No login. No cloud sync. No leaked numbers.

BMR and daily calories Lean shows your resting metabolic rate (the calories you'd burn doing nothing) and your daily energy needs at five activity levels: sedentary, lightly active, moderately active, very active, and extra active. The narrative under the number explains what eating 500 kcal/day under or over means for body composition — without prescribing a diet.

Privacy that actually means something • No account required. Ever. • No personal data sent to our servers. There are no servers. • Every measurement stays on your device. Uninstalling the app deletes everything. • Optional Google AdMob banner ads on the Progress and More tabs only — never on the Calculator. One $2.99 in-app purchase removes them forever.

For honest self-tracking, not medical advice Body-fat estimates from circumference measurements are useful for tracking change over time. They are not a substitute for DEXA, BodPod, or a clinical assessment. If you have a medical concern, see a clinician.