Body Metrics Calculator

This page is a collection of nine small calculators that turn a few tape-measure numbers — height, weight, waist, hip, neck, wrist — into summary statistics about body size and composition. None of them measure anything directly: they are all empirical formulas, regression equations fit to small populations, that produce a single number which is then bucketed into a category (underweight, normal, overweight, obese). Every calculator here should be read as a quick screen, not a verdict — DEXA scans, hydrostatic watches, and blood tests exist precisely because the tape-measure formulas are approximations.

BMI = weight (kg) / height² (m²), a formula cooked up by Adolphe Quetelet in the 1830s and revived in 1972 by Ancel Keys as the "Quetelet index." The WHO cutoffs (international) classify <18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, ≥30 obese (with sub-classes I/II/III for 30–34.9 / 35–39.9 / ≥40). China's Working Group on Obesity in Chinese Adults (COTH) uses tighter thresholds because Asian populations develop metabolic complications at lower BMIs: <18.5 underweight, 18.5–23.9 normal, 24–27.9 overweight, ≥28 obese. With the sample (175 cm, 70 kg male), BMI = 70 / 1.75² = 22.9 kg/m² — WHO Normal Range, China Normal.

BMR (basal metabolic rate) is the calories you burn lying still, fasting, in a dark room at comfortable temperature — basically the cost of running your organs and maintaining body temperature. The page implements three formulas: Mifflin-St Jeor (1990) is the modern default and most accurate for non-obese adults; Harris-Benedict Revised (1984) is older and tends to over-estimate; WHO/FAO (1985) uses piecewise constants by age bracket. With the sample (male, 30 yr, 175 cm, 70 kg), Mifflin returns 10×70 + 6.25×175 − 5×30 + 5 = 1649 kcal/day, Harris-Benedict returns 1696 kcal/day, WHO/FAO (≤30 male) returns 1750 kcal/day. TDEE (total daily energy expenditure) is BMR times an activity multiplier: 1.2 sedentary / 1.375 light / 1.55 moderate / 1.725 active / 1.9 very active. With BMR 1695 and "moderate", TDEE = 2627 kcal/day; the page also reports a ±500 kcal target band for gradual weight change (about 0.5 kg/week, since 1 kg of fat ≈ 7700 kcal).

The U.S. Navy circumference method uses just a tape measure (no calipers, no scales, no DEXA): for men, BF% = 86.010×log₁₀(waist−neck) − 70.041×log₁₀(height) + 36.76; for women, BF% = 163.205×log₁₀(waist+hip−neck) − 97.684×log₁₀(height) − 78.387. With the sample (175 cm, neck 38 cm, waist 85 cm, male), BF% = 86.010×log₁₀(47) − 70.041×log₁₀(175) + 36.76 ≈ 23.5% (Average category for adult males; athletes 6–14%, fitness 14–18%, average 18–25%, above-average ≥25%). For women the categories are shifted up by 6–8 percentage points (essential 14–21%, athletes 21–25%, etc.) because female physiology carries more essential fat for reproductive function. The formula's accuracy is ±3–4% versus DEXA — useful for tracking change over time, less so for absolute numbers.

There is no such thing as "the" ideal weight; each formula gives a different answer because each was fit to a different population for a different purpose. Robinson (1983): 52 kg + 1.9 kg/in (male) above 5 ft; Miller (1983): 56.2 + 1.41; Devine (1974): 50 + 2.3 (originally for gentamicin dosing); Hamwi (1964): 48 + 2.7 (originally for meal planning in diabetes). With the sample (175 cm / 68.9 in male), the four formulas give 68.9, 68.7, 70.5, 72.0 kg, average 70.0 kg. Modern medicine increasingly prefers body-composition goals (specific body fat %, waist circumference) over ideal-weight targets.

Waist-to-hip ratio (WHR = waist / hip) distinguishes apple (android, abdominal fat) from pear (gynoid, gluteofemoral fat) body shapes. Android fat — visceral adipose tissue stored around the liver, pancreas, and intestines — is metabolically active and strongly correlated with type 2 diabetes, cardiovascular disease, and metabolic syndrome. Gynoid fat is more inert. WHO risk thresholds: men ≥0.90 is moderate, ≥1.0 is high; women ≥0.80 is moderate, ≥0.85 is high. With the sample (85 cm waist / 95 cm hip male), WHR = 0.895 (Low Risk, just below the 0.90 cutoff for moderate). The measurement technique matters: waist is measured at the midpoint between the lowest rib and the iliac crest at end-expiration, not at the belly button or belt line; hip is at the widest circumference around the buttocks.

Body surface area (BSA) is the total skin area in m² — used for drug dosing (especially chemotherapy), fluid resuscitation in burns, and cardiac index. Three formulas here: Mosteller (1987) is the simplest and most commonly used today — BSA = √(height_cm × weight_kg / 3600); Du Bois & Du Bois (1916) was the original allometric formula on nine subjects; Haycock (1978) uses different exponents and is preferred for neonates. With the sample (175 cm / 70 kg), all three give BSA ≈ 1.847 m² (Mosteller 1.8447, Du Bois 1.8481, Haycock 1.8468 — agreement to 0.2%). A typical adult BSA is 1.7–2.0 m²; children run smaller, large adults larger.

Lean body mass (LBM) is total weight minus fat mass — muscle, bone, water, organs, connective tissue. The Boer (1984) formula: male LBM = 0.407×weight + 0.267×height − 19.2; female LBM = 0.252×weight + 0.473×height − 48.3. With the sample (male, 175 cm, 70 kg), LBM = 28.49 + 46.725 − 19.2 = 56.0 kg, so fat mass = 70 − 56.0 = 14.0 kg, LBM% = 80.0% (consistent with the Navy BF% above, which said 23.5% fat and thus 76.5% lean — small discrepancy reflects different equation sources and normal measurement noise). LBM is the better predictor of basal metabolic rate than total weight, because muscle is metabolically expensive (~13 kcal/kg/day) while fat is cheap (~4.5 kcal/kg/day). This is why two people of the same weight can have very different BMR.

Body frame size is sometimes estimated by the simple ratio r = height / wrist circumference. The logic: a tall narrow-wristed person has long thin bones (small frame); a short wide-wristed person has stocky bones (large frame). The cutoffs here are: male r > 10.4 small, 9.6–10.4 medium, < 9.6 large; female r > 11.0 small, 10.1–11.0 medium, < 10.1 large. With the sample (male, 175 cm / 17.5 cm wrist), r = 10.0 (Medium Frame). Frame size affects ideal weight ranges: a large-framed person carries more bone and muscle at the same height, so the "ideal" body fat percentage is roughly the same but the "ideal" weight is higher.

• BMI is not a body-fat measure. BMI is a weight-to-height ratio. A muscular athlete can be "overweight" or even "obese" by BMI while having a low body fat percentage. Conversely, a sedentary person can be "normal" BMI with high body fat ("skinny fat"). BMI is a population screen, not an individual verdict.
• BMR is not what you burn in a day. BMR is what you burn at rest, awake but inactive. Total daily expenditure (TDEE) is BMR plus the calories you actually spend on movement, digestion, and thermoregulation. Real activity typically adds 20–90% on top of BMR.
• The Navy body-fat formula is not as accurate as DEXA. It is ±3–4% versus DEXA in most populations, and worse at very low body fat (underestimates) or very high (overestimates). Use it for tracking change over months, not for diagnosing.
• WHR risk cutoffs are population-specific. South Asians and East Asians develop metabolic complications at lower waist circumferences than Europeans; the WHO numbers are Western-derived defaults.

Related tools: Nutrition & Diet for the energy-balance context (macros, fiber, water), Fitness & Exercise for VO₂max and training-zone targets, and Clinical Medicine for the dosing-weight side of BSA and the lab-value side of metabolic risk.