BMI Calculator

Q: What is a good BMI?

For adults, the healthy range is 18.5 to 24.9 on the WHO scale: under 18.5 is underweight, 25–29.9 overweight, and 30 or above falls in the obesity classes. The default example here reads 28.1 — overweight.

Q: How many pounds do I need to lose to reach a healthy BMI?

It depends on your height. At 5'8", the healthy range ends at 163.8 lb, so 185 lb means losing about 21 lb. The calculator shows the exact gap for whatever height you enter.

Height

Weight

lbs

Your BMI

28.1

Category: Overweight
Healthy weight range for your height: 55.2 – 74.3 kg
The same range in pounds: 121.7 – 163.8 lb
Change to reach it: Lose 9.6 kg (21.2 lb)

BMI categories (WHO adult scale)

BMI	Category
Below 18.5	Underweight
18.5 – 24.9	Normal weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity class I
35.0 – 39.9	Obesity class II
40.0 and above	Obesity class III

BMI is a screening ratio, not a diagnosis — it doesn't tell muscle from fat, so muscular build, pregnancy, and age can all skew it. For daily calorie targets, use the TDEE calculator (it accounts for activity level) or the BMR calculator for resting burn. Prefer a target weight in pounds instead of a ratio? Try the ideal weight calculator.

Someone who is 5'8" and 185 lb has a BMI of 28.1, which falls in the overweight range (25–29.9). The healthy BMI range for that height is 121.7 to 163.8 lb, so reaching it would mean losing about 21 lb (9.6 kg). Switch the units to metric — 173 cm and 84 kg — and the same body reads 28.1 too, because both go through the same kg/m² formula.

What BMI is, in one line

BMI = weight (kg) ÷ height (m)²

In US units that's the same thing as 703 × lb ÷ in²; this calculator converts to kilograms and meters first so both unit systems produce identical numbers instead of drifting apart on rounding.

Worked example — the page default, 5'8" (68 in) and 185 lb:

Height: 68 × 2.54 = 172.72 cm → 1.7272 m
Weight: 185 × 0.45359237 = 83.91 kg
BMI: 83.91 ÷ (1.7272 × 1.7272) = 83.91 ÷ 2.983 = 28.1

The number that's more useful than the BMI

A BMI value tells you where you sit; the healthy weight range for your height tells you what to do about it. Both come from the same thresholds — 18.5 and 24.9 — applied to your height:

Height	Healthy weight range (BMI 18.5–24.9)
5'4"	107.8 – 145.1 lb
5'8"	121.7 – 163.8 lb
6'0"	136.4 – 183.6 lb

On the default input, 185 lb sits 21.2 lb above the top of the 5'8" range — that's the gap the calculator reports alongside the BMI. At 130 lb the same person reads 19.8, comfortably inside the range but only about 8 lb from its lower edge.

What BMI doesn't know

BMI was designed for populations, not individuals, and it has well-documented blind spots:

It can't tell muscle from fat. A muscular 5'8" 210 lb person can read "obese" with very little body fat. If you train seriously, the body fat calculator is a better check.
It ignores where fat is carried. Abdominal fat carries more metabolic risk than the same weight carried elsewhere — and BMI sees none of that.
It shifts with age and sex. Older adults typically carry more fat at the same BMI, and women carry more body fat than men at the same value.
It isn't a pediatric measure. Children and teens use age- and sex-specific growth charts, not the adult thresholds on this page.

For those reasons, clinicians use BMI as a screening flag, not a diagnosis: it's a reason to look closer (blood pressure, waist circumference, blood work), not a verdict.

How to use this calculator

Pick US or metric units.
Enter height — feet and inches, or centimeters.
Enter weight — pounds or kilograms.
Read your BMI, the WHO category it falls in, and the healthy weight range for your height.
Read the gap: how many pounds or kilograms to the nearest edge of the healthy range, and in which direction.

Frequently asked questions

What is a good BMI?

For adults, the healthy range is 18.5 to 24.9 on the WHO scale: under 18.5 is underweight, 25–29.9 overweight, and 30 or above falls in the obesity classes. The default example here reads 28.1 — overweight.

How many pounds do I need to lose to reach a healthy BMI?

It depends on your height. At 5'8", the healthy range ends at 163.8 lb, so 185 lb means losing about 21 lb. The calculator shows the exact gap for whatever height you enter.

Is BMI accurate if I'm muscular?

Less so. BMI can't distinguish muscle from fat, so muscular people often read high — a 5'8" lifter at 210 lb may have a BMI over 30 with low body fat. Use a body-fat method instead if you train seriously.

Is BMI different for men and women?

The formula is identical; the interpretation isn't quite. At the same BMI, women typically carry more body fat than men, and older adults more than younger ones — which is why the thresholds are a screening tool, not a body-composition measurement.

Can I use this for my child?

No. Children and teens are assessed on age- and sex-specific BMI percentile charts, not the fixed adult thresholds used here. Use your pediatrician's growth chart.

Why does the calculator use kg/m² even when I enter pounds?

So both unit systems give the same answer. Converting to kilograms and meters first means 5'8"/185 lb and 173 cm/84 kg produce the same 28.1, rather than two figures that differ by rounding.

Data sources: BMI is defined as weight in kilograms divided by height in meters squared. The category thresholds used here are the WHO adult standards (underweight < 18.5, normal 18.5–24.9, overweight 25–29.9, obesity class I 30–34.9, class II 35–39.9, class III ≥ 40), which the CDC also uses for adults. The healthy weight range is those 18.5 and 24.9 thresholds applied to the height you enter. Unit conversions use the exact definitions 1 lb = 0.45359237 kg and 1 in = 2.54 cm. Every figure on this page was produced by this calculator and can be reproduced with the same inputs.

Disclaimer: BMI is a population screening tool, not a diagnosis or a body-composition measurement — it cannot distinguish muscle from fat, fat distribution, age, or sex. This calculator is for general reference only and is not medical advice. If you have a medical condition, are pregnant or nursing, or are planning significant weight changes, talk to a doctor or registered dietitian. Related tools: ideal weight calculator, body fat calculator, TDEE calculator, all health calculators.