Quick answer
BMI Calculator: what it calculates
BMI Calculator calculates BMI from pounds or kilograms, height, and unit system. The visible formula is BMI = kg / meters^2; US equivalent = pounds / inches^2 x 703.
Health Calculators
BMI Calculator
Use this BMI calculator to estimate body mass index, BMI category, and a healthy BMI weight range from pounds and feet/inches or kilograms and centimeters.
Last reviewed June 6, 2026Source note includedPlanning estimateNo expert review claimed
Live calculator
BMI calculator
BMI25.8
Category: Overweight. BMI is a screening number, not a diagnosis.
Healthy BMI range129 - 174 lb
Approximate weight range for BMI 18.5 to 24.9 at this height.
Height70 inches
70 in / 177.8 cm used with weight to calculate BMI.
Use BMI as a screening estimate only. Body composition, age, pregnancy, athletic build, medical history, and clinician guidance can change the right interpretation.
ResultBMI
InputsPounds or kilograms, Height, Unit system
FormulaBMI formula
Formula
BMI formula
BMI = kg / meters^2; US equivalent = pounds / inches^2 x 703BMI is a screening measure and does not directly measure body fat or health. The calculator supports US and metric inputs.
How to use
Steps
- Choose pounds or kilograms.
- Enter weight and height in the selected unit system.
- Read the BMI number and category.
- Use the healthy range as a broad reference, not a medical diagnosis.
Example
Sample calculation
Weight180 lb / 81.6 kg
Height5 ft 10 in / 177.8 cm
BMI25.8
Calculator use
Best for
- Estimating adult body mass index from height and weight.
- Checking the CDC adult BMI category and broad healthy-weight reference range.
- Using BMI as one screening number before considering body composition, age, pregnancy, athletic context, or medical history.
- Preparing a simple reference point for a clinician conversation, not a diagnosis.
Before relying on it
Check first
- Treating BMI as a direct body-fat measurement or a full health assessment.
- Applying adult BMI categories to children or teens, who use age and sex percentiles.
- Ignoring muscle mass, pregnancy, older age, medical conditions, or other context that can make BMI misleading.
- Changing diet, medication, or training based on BMI alone without appropriate professional context.
Details
What to know before using the result
These notes make the assumptions explicit, especially where the same search query can mean slightly different things.
Adult scopeAdults 20 and older
Adult BMI categories are different from child and teen BMI interpretation, which uses age and sex percentiles.
Screening useNot a diagnosis
BMI is one health indicator. It does not directly measure body fat, fitness, medical history, lab markers, or health risk by itself.
Category limitsBody composition matters
BMI can be misleading for muscular people, older adults, pregnancy, and some medical situations.
Benchmarks
How to read the result
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions. Benchmark ranges are broad planning heuristics unless this page names a specific source for the range.
Under 18.5: Underweight.
A low BMI can be worth discussing with a qualified professional.
18.5 - 24.9: Healthy range.
Often used as the general adult BMI reference range.
25+: Above range.
BMI does not account for muscle mass, body composition, age, or pregnancy.
Calculator accuracy
Methodology and assumptions
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Formula
BMI = kg / meters^2; US equivalent = pounds / inches^2 x 703
Inputs used
Pounds or kilograms, Height, Unit system
Limitations
BMI uses only height and weight. It does not directly measure body fat, muscle mass, distribution of weight, lab markers, medical risk, pregnancy status, or child/teen percentiles.
Last reviewed
June 6, 2026
Cite this page
Toolkit Shelf. BMI Calculator. Last reviewed June 6, 2026. https://toolkitshelf.com/tools/bmi-calculator
FAQ
Common questions
What is BMI?
BMI stands for body mass index. It compares weight with height to produce a screening number using kg/m² or the equivalent US formula.
Is BMI a medical diagnosis?
No. BMI is a broad screening estimate and should not replace medical advice or a full health assessment.
Does BMI work for athletes?
BMI can be misleading for muscular people because it does not distinguish muscle from fat.
What are BMI's biggest limitations?
BMI does not directly measure body fat, muscle mass, pregnancy status, age-related changes, or individual health risk. It is a screening number, not a diagnosis.
Is BMI interpreted the same for children and adults?
No. Adult BMI categories are for adults 20 and older. Children and teens are interpreted with age and sex percentiles.
When can BMI be misleading?
BMI can be misleading for muscular people, pregnancy, older adults, and some medical situations because it only uses height and weight.