If a scale reading and a tape measure are all you have, BMI is the fastest way to see where you stand. Here's how the calculation actually works in pounds and inches, what the CDC/WHO categories mean, and how BMI connects to a healthy weight range and daily calorie needs.
How is BMI calculated in pounds and inches?
Quick answerBMI = weight (lb) × 703 ÷ height (in)². For a 176 lb adult who is 5'9" (69 inches): 176 × 703 ÷ 69² = 123,728 ÷ 4,761 = 26.0.
The 703 constant exists purely to convert pounds and inches into the same metric ratio used worldwide — weight in kilograms divided by height in meters squared. Both formulas describe the same idea: how much you weigh relative to how tall you are, squared. Squaring the height matters because weight tends to scale with the square (not the simple length) of a person's frame, which is why a taller person and a shorter person at the same BMI can look quite different on a scale.
Working through it by hand only takes four steps: convert feet and inches into total inches, square that number, multiply your weight in pounds by 703, then divide by the squared height. A BMI calculator does the same arithmetic instantly and also plots the result against the standard categories, which is the part most people actually want.
What do the CDC/WHO BMI categories mean?
Quick answerThe CDC and WHO treat 18.5–24.9 as a normal, healthy BMI for most adults. Below 18.5 is underweight, 25–29.9 is overweight, 30–34.9 is obesity class 1, 35–39.9 is class 2, and 40+ is severe obesity (class 3).
These bands were built from population health data linking BMI to average health outcomes, so they describe group tendencies rather than a verdict on any one individual. A BMI of 26.0, like the example above, sits just inside the "overweight" band — a signal worth noting, not a diagnosis.
Example BMI calculations (adult, US units)
| Height | Weight | BMI | Category |
|---|
| 5'5" (65 in) | 132 lb | 22.0 | Normal |
| 5'7" (67 in) | 154 lb | 24.1 | Normal |
| 5'9" (69 in) | 176 lb | 26.0 | Overweight |
| 5'11" (71 in) | 198 lb | 27.6 | Overweight |
| 5'9" (69 in) | 209 lb | 30.9 | Obese (Class 1) |
Note: the same weight lands in a higher BMI category on a shorter frame — height, not just weight, drives the category boundary.
How do you find your healthy weight range?
Quick answerRearrange the formula to find the weight matching a BMI of 18.5 and 24.9 at your height: weight (lb) = BMI × height (in)² ÷ 703. For someone 5'7" (67 in), that works out to roughly 118–159 lb.
Beyond the BMI-based range, clinical "ideal weight" formulas — Devine, Robinson, Miller, and Hamwi — each estimate a single target figure from height and sex, developed decades ago mostly for medication dosing rather than aesthetics. None of them is more "correct" than the others; they're commonly averaged together to smooth out individual formula quirks.
Reverse BMIInstead of computing BMI from weight, reverse BMI answers "what weight gives me a chosen BMI at my height?" — useful for setting a concrete weight target rather than working in abstract BMI units.
How does BMI connect to daily calorie needs?
Quick answerBMI tells you where you stand; TDEE (total daily energy expenditure) tells you how to move. TDEE = BMR (via the Mifflin-St Jeor equation) × an activity multiplier from 1.2 (sedentary) to 1.9 (very active).
Say a hypothetical 30-year-old man, 5'9" and 176 lb, moderately active, calculates a TDEE of roughly 2,600 calories — this is an illustrative example only, not a personal recommendation. Eating near that number tends to maintain weight; eating consistently a few hundred calories below it is the common approach toward gradual weight loss, and above it toward gradual gain. Because BMI can't separate muscle from fat, someone who lifts weights regularly may want to weigh a body-fat-percentage estimate (for example, the U.S. Navy tape-measure method) alongside their BMI rather than relying on BMI alone.
Frequently asked questions
How do you calculate BMI in pounds and inches?
BMI = weight (lb) × 703 ÷ height (in)². For example, a 176 lb adult who is 5'9" (69 inches) has a BMI of 176 × 703 ÷ 69² = 123,728 ÷ 4,761 = 26.0. In metric units the same result comes from kilograms divided by height in meters squared (kg ÷ m²).
What BMI range counts as healthy?
The CDC and WHO consider 18.5 to 24.9 a healthy BMI for most adults. Below 18.5 is classified as underweight, 25 to 29.9 as overweight, and 30 or above as obese. The exact healthy weight in pounds depends on your height.
Does BMI account for muscle mass?
No. BMI only compares weight to height, so it cannot distinguish muscle from fat. A muscular person can register as "overweight" by BMI while having low body fat, and someone with low muscle mass can show a "normal" BMI despite a higher body fat percentage. It works best as a quick screening number, not a full diagnosis.
How does BMI relate to ideal weight and daily calories?
Ideal weight is often set as the weight range matching a BMI of 18.5–24.9 for your height, sometimes refined with formulas like Devine or Hamwi. Once you have a target weight, daily calorie needs are estimated separately with the Mifflin-St Jeor equation for BMR, multiplied by an activity factor to get TDEE — the calorie level that maintains, or a few hundred calories below it to help move toward that target.
Is a BMI calculator a substitute for medical advice?
No. A BMI calculator is an informational screening tool based on height and weight only. It does not replace an evaluation from a doctor or registered dietitian, especially for decisions about weight loss, weight gain, or underlying health conditions.