BMI Calculator

Calculate your Body Mass Index (BMI) to check if your weight is in a healthy range. Enter your height and weight to see your BMI and health category.

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About BMI

  • BMI = Weight (kg) / Height (m)²
  • BMI does not directly measure body fat, so use it as a reference only.
  • Athletes with high muscle mass may have elevated BMI readings.
  • Consult a healthcare professional for accurate health assessment.

What is a BMI Calculator?

A BMI (Body Mass Index) calculator is a health screening tool that estimates body fat based on your height and weight. The formula, BMI = weight (kg) / height (m)^2, produces a single number that healthcare professionals use worldwide to categorize weight status as underweight, normal, overweight, or obese. It is one of the most accessible starting points for understanding your weight in relation to your height.

How It Works

BMI (Body Mass Index) divides weight (kg) by height (m) squared. Formula: BMI = weight ÷ (height × height). For example, 70kg at 175cm: BMI = 70 ÷ (1.75 × 1.75) = 22.86. WHO classifies under 18.5 as underweight, 18.5-24.9 as normal, 25-29.9 as overweight, and 30+ as obese. Asia-Pacific criteria consider 23+ as overweight.

Step-by-Step Guide

Getting a reading takes under a minute — the calculator only asks for two measurements.

  1. Choose your preferred unit system with the buttons at the top. Imperial (ft/lb) is selected by default on this page; switch to Metric (cm/kg) if you think in centimeters and kilograms.
  2. Enter your height. In imperial mode you get separate ft and in boxes (for example, 5 and 10 for someone who is 5'10"); in metric mode a single cm field appears.
  3. Enter your weight in the lb or kg field. Decimals are accepted, so 150.5 lb works fine.
  4. Click Calculate. Your BMI number, weight category, a position marker on the gauge, and your healthy weight range all appear below the button.

What Your Result Means

The large number in the center is your BMI, and the label beneath it tells you which of the four WHO categories you fall into. The colored gauge places a marker along the 15-to-40 scale so you can see how close you sit to a category boundary — someone at 24.8 is technically "normal" but only a fraction away from the overweight line, which is useful context a label alone doesn't give you.

Here's the arithmetic behind a sample result. Say you enter 5 ft 10 in and 180 lb. The tool converts these to about 1.78 m and 81.6 kg, squares the height (1.78 × 1.78 = 3.16), and divides: 81.6 ÷ 3.16 = 25.8. That lands just inside the overweight band (25 to 29.9), so the yellow category card lights up.

The Healthy Weight Range box at the bottom runs the formula in reverse: it multiplies your squared height by 18.5 and by 24.9. For the same 5'10" person, that works out to roughly 129 to 174 lb. If you're setting a weight goal, aiming anywhere inside this band is more realistic than chasing a single "ideal" number.

Frequently Asked Questions

Is BMI accurate for people who lift weights?

Not particularly. Muscle is denser than fat, so a muscular person can register as overweight or even obese while carrying very little body fat. BMI has no way of telling the two apart because the formula only sees total weight. If you train regularly and your BMI looks alarming, a body fat percentage measurement or waist circumference will give you a far more honest picture.

Why do some countries use different BMI cutoffs?

Research on Asian populations found that health risks like type 2 diabetes and cardiovascular disease begin to rise at lower BMI values than in Western populations, partly due to differences in body fat distribution. The WHO therefore endorsed lower Asian-Pacific thresholds for overweight and obesity. This calculator displays the standard international categories, so if you live in a country using the Asian-Pacific scale, your official classification may differ from what you see here.

Does age affect how I should read my BMI?

Yes. Older adults naturally lose muscle mass, meaning a "normal" BMI can hide low muscle and relatively high fat, and some studies suggest slightly higher BMI values are associated with better outcomes in seniors. Children and teenagers should never use adult categories at all — pediatric BMI is interpreted through age- and sex-specific percentile charts instead.

Is being underweight a health concern too?

It can be. A BMI below 18.5 is associated with nutritional deficiencies, weakened immunity, reduced bone density, and fertility issues. Unintentional weight loss deserves the same medical attention as weight gain, so if your BMI is persistently low without an obvious explanation, it's worth discussing with a healthcare provider.

Can I use this during pregnancy?

Standard BMI categories aren't meant for pregnancy, since weight gain from the baby, placenta, and increased blood volume is expected and healthy. Clinicians instead use your pre-pregnancy BMI to recommend a target range of weight gain for the pregnancy. Any weight-related decisions during this period belong in a conversation with your doctor or midwife.

What is the waist-to-height ratio, and should I check it too?

It's a complementary metric many clinicians like because it captures where weight sits, not just how much there is: divide your waist circumference by your height in the same units, and a result under roughly 0.5 is the commonly cited target. Two people with an identical BMI can carry fat very differently, and abdominal fat is the kind most strongly linked to metabolic risk, so a normal BMI paired with a high waist-to-height ratio is worth raising with a doctor. All it takes is a tape measure, which makes it an easy habit to pair with this calculator.

Why Two People With the Same BMI Can Look Completely Different

Picture two people who are both 5'9" and 170 lb — their BMI is identical at about 25.1. One might be an amateur rugby player with broad shoulders and low body fat; the other might rarely exercise and carry most of that weight around the midsection. The formula treats them as the same person, yet their actual health risks could differ dramatically, because it's visceral fat — not weight itself — that correlates most strongly with metabolic disease.

This is why clinicians describe BMI as a screening tool, not a diagnostic one. It's excellent for spotting trends across large populations and for flagging when an individual's number drifts over time, but it was never designed to summarize one person's health in isolation. Use the result here as a starting point: if your number sits outside the normal band or has shifted noticeably since your last check, treat that as a prompt to look at habits, get a waist measurement, or book a check-up rather than as a final judgment.

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Further Reading