A complete guide — with the US (pounds/inches) formula, CDC/WHO categories, ideal weight, and calorie needs.
Body Mass Index (BMI) is a simple screening measure that compares your weight to your height to estimate whether you fall in a healthy weight range. In US units it's calculated as BMI = weight (lb) × 703 ÷ height (in)²; in metric units it's simply kg ÷ m² — both give the same result. BMI is widely used in health screenings because it only requires a scale and a tape measure, but it is a starting point, not a full diagnosis: it does not directly measure body fat or account for muscle mass.
How do you calculate BMI in pounds and inches?
Quick answerBMI = weight (lb) × 703 ÷ height (in)². First convert your height to inches (5'9" = 5×12+9 = 69 in), square it (69² = 4,761), multiply your weight by 703, then divide. For a 176 lb, 5'9" adult: 176 × 703 ÷ 4,761 = 26.0, which falls in the 25–29.9 "overweight" range.
- Height in inches — feet × 12 + inches: 5'9" = 69 in.
- Height squared — 69 × 69 = 4,761 in².
- BMI — weight × 703 ÷ height²: 176 × 703 ÷ 4,761 = 26.0.
- Interpretation — match the value against the CDC/WHO table below.
What should my BMI be? CDC/WHO categories
Quick answerThe CDC and WHO consider 18.5–24.9 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 obesity class 2, and 40+ is severe obesity (class 3). Your healthy weight in pounds depends on your height — for example, about 118–159 lb for someone 5'7" tall.
If you're planning to lose or gain weight, start by setting a target inside this healthy range and then build a daily calorie plan around it. See the Daily calorie needs mini calculator below for your BMR and TDEE.
How do you find your ideal weight?
Quick answerThe most reliable benchmark is the weight range matching a BMI of 18.5–24.9 for your height. In addition, classic clinical formulas — Devine, Robinson, Miller, and Hamwi — each estimate a single "ideal weight" figure in pounds based on height and sex. The Ideal weight calculator below shows both at once.
Why do body fat percentage and daily calories matter too?
Quick answerBecause BMI can't tell muscle from fat, body fat percentage gives a fuller picture for athletes or older adults. For weight management, you also need TDEE (total daily energy expenditure): BMR × activity multiplier. Eating roughly 500 kcal below TDEE targets about 1 lb of loss per week; 500 above targets about 1 lb of gain.