BMI and BMR Calculator

Features

• BMI graded by both the Chinese and the WHO standard, with an explanation of why they differ
• BMR via Mifflin-St Jeor, with the male and female constants kept apart
• TDEE across five activity levels, with the factor written on each option
• A healthy weight range for your height (one per standard) — easier to check against a scale than an index
• ⚠️ Two body-fat estimates side by side: the tape method (US Navy formula, needs a tape measure) and Deurenberg (BMI, age and sex only, so anyone gets a figure). The gap between them is informative — the wider it is, the further your build is from average
• ⚠️ The tape method computes nothing when a measurement is missing, rather than substituting a default and producing a wrong value that looks normal; a waist no larger than the neck (the usual mix-up) is called out explicitly
• Body-fat banding (low / athletic / fitness / average / high) with different boundaries for men and women — one percentage means different things for each
• Extreme inputs are clamped and NaN falls back to defaults, so nothing absurd comes out
• Everything updates live as you change the options; no button to press
• The page states who the numbers do not apply to instead of hedging
• Computed locally; no body data is uploaded

How to use

1. Enter your height, weight and age
2. Pick sex (the BMR formula needs it) and an activity level
3. BMI, both standards’ verdicts and the daily burn appear immediately
4. Change the weight to see how the numbers move

FAQ

Why two BMI standards? Which one should I use?

Because the two really do draw the lines in different places, and both remain in official use. Chinese standard (WS/T 428-2013): underweight <18.5, normal 18.5–23.9, overweight 24–27.9, obese ≥28. WHO: underweight <18.5, normal 18.5–24.9, overweight 25–29.9, obese ≥30. The difference exists because at the same BMI, Asian populations tend to have a higher body-fat percentage and metabolic risk, so the Chinese cut-offs sit lower. Which applies to you depends on your region and which standard your clinic uses — so both are shown rather than one being chosen for you.

What is the difference between BMR and TDEE?

BMR (basal metabolic rate) is what you burn lying completely still, keeping the body running; it is the bulk of the day’s total. TDEE (total daily energy expenditure) is that multiplied by an activity factor — what you actually burn in a day. The factors here are the usual five (1.2 to 1.9). Note that TDEE carries more error than BMR: activity level is hard to self-assess, and most people overestimate it.

The BMR here differs from my smart scale. Which is right?

Both are estimates, and they estimate in completely different ways. This formula looks only at height, weight, age and sex; a body-composition scale measures bioelectrical impedance and infers from it. Either can be off by ±10% or more. The accurate method is indirect calorimetry (measuring respiratory gas exchange), which needs a lab. So treat these numbers as useful for trends and relative comparisons, not as a precise target.

What are the obvious weaknesses of BMI?

The famous one is that it cannot tell muscle from fat. Two people with the same BMI — a fitness trainer and a desk worker — can differ twofold in body fat while BMI says the same thing, which is why athletes are routinely graded “overweight”. It also says nothing about where the fat is: at equal BMI, a larger waist carries more risk. That is why a healthy weight range is given as well — checking a number against a scale is more tangible than checking an index.