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BMI Calculator | Measure BMI and See Weight Category

A BMI calculator measures Body Mass Index — your weight in kilograms divided by the square of your height in metres. It is a screening tool the WHO uses to flag potential underweight, overweight, or obesity in adults aged 20 and older. BMI does not measure body fat directly, so use it alongside waist circumference for a full picture.

Last updated: June 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

BMI weight categories use the World Health Organization (WHO) classification for adults:

BMI range	Weight category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity (class 1)
35.0 – 39.9	Obesity (class 2)
40.0 and above	Severe obesity (class 3)

monitor_weight WHO classes

See your BMI category against the WHO thresholds: underweight, normal, overweight, obesity class I, II, or III.

straighten Healthy range

See the weight range that corresponds to a normal BMI for your height — the goal range, not a specific target weight.

fitness_center Athlete caveat

Muscular bodies can score "overweight" despite low body fat. Combine BMI with waist circumference for a fuller picture.

public Asian thresholds

WHO recommends lower cut-points (overweight ≥ 23, obese ≥ 27.5) for some Asian populations due to higher cardiometabolic risk.

Interpretation guide

The healthy-weight range (BMI 18.5–24.9) for common heights:

Height	Healthy weight (lb)	Healthy weight (kg)
5'0" (152 cm)	95 – 127 lb	43 – 58 kg
5'4" (163 cm)	108 – 145 lb	49 – 66 kg
5'8" (173 cm)	122 – 164 lb	55 – 74 kg
6'0" (183 cm)	137 – 184 lb	62 – 83 kg
6'4" (193 cm)	152 – 205 lb	69 – 93 kg

BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat, so it can overstate body fat for athletes and understate it for older adults with low muscle mass. Pair it with waist circumference and a clinician’s advice.

lightbulb A real-world example — a 5'10" adult weighing 180 lb

You're 5'10" (178 cm / 1.78 m) and weigh 180 lb (81.6 kg). Enter those values in the form above and pick the Imperial unit option.

Result: BMI = 25.8. This places you in the lower end of the "overweight" range (25.0–29.9) per the WHO classification.

What this means: BMI is a screening tool, not a diagnosis. At 5'10", 180 lb, an athletic build with above-average muscle mass will often land in the "overweight" BMI band even when body-fat percentage is healthy. If your number surprises you, follow up with a body-fat measurement (waist circumference, DEXA scan, or our body-fat calculator) and discuss with your doctor — they look at BMI alongside blood pressure, glucose, and family history before drawing any conclusion.

Formula & methodology

Formula: BMI = weight(kg) / height(m)²

How BMI is calculated

Body Mass Index uses the formula BMI = weight (kg) / height (m)². In imperial units, multiply by 703 to use pounds and inches: BMI = (weight (lb) / height (in)²) × 703.

Example: 70 kg, 1.75 m

BMI = 70 / (1.75 × 1.75) = 22.86 → "Normal weight"

WHO classification (adults ≥ 20 years)

BMI	Category
< 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	Obesity Class III

Limitations

BMI does not distinguish muscle from fat, so highly muscular athletes can be classified as overweight despite low body fat. It is also less accurate for elderly people, children (use BMI percentile), and people of Asian descent (lower thresholds apply). For a fuller picture, combine BMI with waist circumference, body-fat percentage, and clinical assessment.

Source & review

Classification follows the World Health Organization (WHO) BMI Classification. Reviewed quarterly against the latest WHO guidance.

How to use the BMI Calculator

Enter your height and weight in either metric or imperial units — the tool converts automatically — and press calculate. BMI = weight(kg) ÷ height(m)², which is the weight-to-height ratio used by the World Health Organization's adult classification: below 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30+ is obese. A 175 cm, 75 kg person has a BMI of 24.5, at the top of the healthy range.

Interpreting your result

BMI is a screening tool, not a diagnosis — it correlates with body fat at the population level but does not measure body composition directly. Muscular athletes often register as overweight despite low body fat, and older adults can be 'normal' BMI while carrying unhealthy fat. The clinical picture combines BMI with waist circumference, blood pressure, blood sugar, and lifestyle. In children, BMI is read against age-and-sex percentiles rather than fixed cut-offs, because body composition changes with growth.

Common mistakes to avoid

The most common error is treating BMI as a measure of body fat — it is a weight-for-height index, and the same BMI can hide very different body compositions. Second, using imperial units without conversion in the formula — the tool converts, but doing it by hand requires kg and metres. Third, ignoring ethnicity and build: WHO thresholds are population averages, and some groups carry different metabolic risk at the same BMI. Finally, using a single BMI reading to make medical decisions — trends over time and waist measurement are more informative.

Tips for best results

Weigh yourself in the morning for consistent readings and track the trend over months, not single days. Combine BMI with a tape measure around the waist: a waist over 94 cm (men) or 80 cm (women) adds independent health risk even at normal BMI. For athletes and bodybuilders, prefer body-fat percentage or waist-to-height ratio over BMI. Recalculate after significant weight changes, and remember that small changes in diet and activity move BMI slowly but sustainably — the goal is the healthy band, not an arbitrary number.

Authoritative source: World Health Organization

Frequently asked questions

What is a healthy BMI?

The BMI Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. A BMI calculator measures Body Mass Index — your weight in kilograms divided by the square of your height in metres. It is a screening tool the WHO uses to flag potential underweight, overweight, or obesity in adults aged 20 and older. BMI does not measure There is no limit on usage, and it works on any device.

How do I calculate my BMI?

Divide your weight in kilograms by your height in metres squared (kg ÷ m²). In imperial units, multiply weight in pounds by 703, then divide by height in inches squared. For example, 70 kg at 1.70 m gives a BMI of 24.2.

Is BMI accurate for everyone?

No. BMI is a quick screening measure and does not separate muscle from fat. It can read high for muscular athletes and low for older adults with reduced muscle, and it is not used the same way for children, pregnant people or the very elderly.

What does my BMI category mean?

Your category estimates whether your weight may raise health risks. A higher BMI is linked to greater risk of conditions such as type 2 diabetes and heart disease, but BMI is only one part of an overall health picture.

What is a healthy weight for my height?

The healthy BMI band of 18.5–24.9 converts to a weight range: for a 175 cm person, roughly 57–76 kg (126–168 lb). Calculate the range with healthy weight = 18.5 × height(m)² to 24.9 × height(m)². The calculator shows your weight position within that band, and you can read the exact healthy range for your height from the result.

What does the BMI Calculator do?

A BMI calculator measures Body Mass Index — your weight in kilograms divided by the square of your height in metres. It is a screening tool the WHO uses to flag potential underweight, overweight, or obesity in adults aged 20 and older. BMI does not measure. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.

What formula does the BMI Calculator use?

The BMI Calculator uses the standard BMI = weight(kg) / height(m)². You enter your values, and the calculator applies the formula step by step, showing the working so you can verify the math and understand how the result is derived rather than trusting a black box.

Is the BMI Calculator free and private?

Yes — the BMI Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.

How accurate is the BMI Calculator?

The BMI Calculator applies the standard formula: BMI = weight(kg) / height(m)². It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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