BMI Calculator

One number. Decades of arguments. Let's get yours.

Use this free BMI calculator to find your Body Mass Index from height (inches) and weight (pounds). Enter two numbers, click once, and get your BMI plus the category the chart puts you in: underweight, normal, overweight, or obese.

BMI is a screening tool from 1832 that has survived because it is fast, free, and requires no equipment beyond a scale and honesty. It says nothing about muscle, bone density, or how many stairs you can climb without regretting your life. We calculate it accurately, then keep the commentary proportional.

What This BMI Calculator Does

Calculates BMI from imperial units (inches and pounds) using the standard CDC formula
Places the result in the WHO/CDC adult BMI categories
Gives you a baseline number to track over time — trends matter more than any single reading
Roasts the number, lightly, because a spreadsheet would have been rude anyway

How to Use the BMI Calculator

Inputs:

Height — in inches (5'10" = 70 in). Metric users: cm ÷ 2.54
Weight — in pounds. Metric users: kg × 2.205

Steps:

Enter your height in inches
Enter your weight in pounds — the real one, not the driver's license one
Click Calculate
Read your BMI score and category, then read the Reality Check below before doing anything drastic

How the Calculation Works

BMI = 703 × weight (lb) ÷ height (in)² BMI = weight (kg) ÷ height (m)²

703 is the conversion factor that makes the imperial version match the metric definition
Under 18.5 = underweight · 18.5–24.9 = normal · 25–29.9 = overweight · 30+ = obese (adult ranges)
Children and teens use age- and sex-specific percentiles, not these cutoffs — this calculator is for adults

Worked Example: 5'10", 180 lb

Height = 70 in → 70² = 4,900
180 ÷ 4,900 = 0.03673
0.03673 × 703 = 25.8
Category: overweight — by 0.9 points. A large breakfast could have changed the label. That is how blunt this tool is.

Tips (From People Who Have Made These Mistakes)

Weigh yourself at the same time of day (morning, after the bathroom, before coffee) if you want comparable numbers
If you lift weights regularly, expect BMI to overstate your fat — muscle is denser than fat and BMI cannot tell them apart
Pair BMI with waist circumference or body fat percentage; together they say far more than either alone

Frequently Asked Questions

What is a healthy BMI?

For adults, 18.5 to 24.9 is the "normal weight" range. It is a population-level guideline, not a personal verdict — many healthy people sit slightly outside it.

Is BMI accurate for athletes?

Not really. BMI only knows total weight, so muscular people often score "overweight" while carrying very little fat. If you train hard, use a body fat calculator or waist-to-height ratio instead.

How do I calculate BMI with kg and cm?

Convert first: kg × 2.205 = lb, cm ÷ 2.54 = in. Or use the metric formula directly: kg ÷ (m × m). 80 kg at 1.78 m → 80 ÷ 3.17 = 25.2.

Does BMI differ for men and women?

The formula and the adult categories are identical. Women naturally carry more body fat at the same BMI, which is one of the reasons BMI is a rough screen rather than a diagnosis.

What BMI is considered obese?

A BMI of 30 or higher. Class I is 30–34.9, Class II 35–39.9, Class III 40+. These are the cutoffs doctors use to decide whether to look closer, not the closer look itself.

Mini Roast Disclaimer

We roast the number, not you. BMI already judges everyone equally badly; we just add a punchline.

Reality Check

BMI ignores muscle, bone, age, sex, ethnicity, and where your fat actually sits. It is useful for spotting trends and starting conversations with a doctor, and useless for deciding whether you are healthy on its own. Treat it as a smoke detector, not a diagnosis.

BMI Calculator (Body Mass Index)

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