BMI under 18.5 is underweight, 18.5–24.9 healthy, 25–29.9 overweight and 30+ obese. BMI ignores muscle vs fat, so very muscular people can read high — use it as a guide, not a verdict.

What are common bmi mistakes?

Treating BMI as body fat \u2014 very muscular people read high despite low fat.

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BMI Calculator

Q: What is BMI?

A BMI (Body Mass Index) calculator estimates whether your weight is in a healthy range for your height. It is a quick, widely used screening number — not a diagnosis.

Q: How is BMI calculated?

It divides your weight by the square of your height, giving a single figure that maps to standard categories. The tool also shows the healthy weight range for your height. Formula: BMI = weight (kg) ÷ height (m)^2.

Q: Is the BMI Calculator free to use?

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

Q: How accurate is the BMI Calculator?

BMI Calculator uses the standard bmi formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Q: Do you store my inputs?

No. The BMI Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Q: Can I use the BMI Calculator on mobile?

Yes — the interface is fully responsive and works on phones, tablets and desktops.

Q: What are common mistakes to avoid?

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

Calculate your Body Mass Index in seconds.

Losing weightStep 1 of 5

Best for: Use it for a quick health check, to set a target weight range, or to track changes over time. For health decisions, consult a professional.

Complete guide

See benchmark ranges Why this result happened View assumptions

Input

Height (cm)Weight (kg)Units

How it's calculated & sources

Method: BMI = weight (kg) ÷ height (m)². Categories follow the WHO classification for adults (Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30).

Sources: World Health Organization & U.S. CDC. Reviewed June 2026. BMI is a screening measure, not a diagnosis — it does not distinguish muscle from fat.

Key assumptions

Uses the WHO BMI formula
Does not distinguish muscle from fat

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

Continue your journey

Where people usually head next.

％

Percentage Calculator

Find percentages, increases and decreases.

Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is BMI?: A BMI (Body Mass Index) calculator estimates whether your weight is in a healthy range for your height. It is a quick, widely used screening number — not a diagnosis.
Why does BMI matter?: BMI under 18.5 is underweight, 18.5–24.9 healthy, 25–29.9 overweight and 30+ obese. BMI ignores muscle vs fat, so very muscular people can read high — use it as a guide, not a verdict.
How is BMI calculated?: It divides your weight by the square of your height, giving a single figure that maps to standard categories. The tool also shows the healthy weight range for your height. Formula: BMI = weight (kg) ÷ height (m)^2.
What is a good bmi?: 18.5-24.9 (healthy range)
What are common bmi mistakes?: Treating BMI as body fat \u2014 very muscular people read high despite low fat.
When should you use the BMI Calculator?: Use it for a quick health check, to set a target weight range, or to track changes over time. For health decisions, consult a professional.

What is the BMI Calculator?

A BMI (Body Mass Index) calculator estimates whether your weight is in a healthy range for your height. It is a quick, widely used screening number — not a diagnosis.

How the BMI Calculator works

It divides your weight by the square of your height, giving a single figure that maps to standard categories. The tool also shows the healthy weight range for your height.

BMI = weight (kg) ÷ height (m)^2

weight — Body weight in kilograms
height — Height in metres (squared)

Component definitions

The parts that drive this result and what each one contributes.

Weight — Body weight (kg or lb).
Height — Used squared in the BMI formula.

Benchmark reference

What counts as poor, average or excellent for this metric.

Body Mass Index

Poor	30+ (obese)
Below average	<18.5 (underweight)
Average	18.5-24.9 (healthy)
Above average	25-29.9 (overweight)

Source: World Health Organization (WHO) · Updated June 2026

Typical values

Body Mass Index:: 18.5-24.9 (healthy range)

Common interpretation errors

Using BMI for athletes or very muscular people
Ignoring body composition
Using adult BMI for children

What impacts results most

1.
Weight (High impact)BMI rises directly with body weight.
2.
Height (Medium impact)BMI falls with the square of height.

Key assumptions

Uses the WHO BMI formula
Does not distinguish muscle from fat

What's a typical value?

A BMI of 18.5\u201324.9 is the healthy range for most adults. Below 18.5 is underweight; 25\u201329.9 overweight; 30+ obese. BMI is a screening tool, not a diagnosis.

BMI categories (WHO)

Below 18.5	Underweight
18.5 \u2013 24.9	Healthy weight
25.0 \u2013 29.9	Overweight
30.0 \u2013 34.9	Obesity class I
35.0 \u2013 39.9	Obesity class II
40.0 and above	Obesity class III

Worked example

Inputs: Weight 70 kg, height 1.75 m Calculation: BMI = weight ÷ height² Result: 22.9 (healthy, 18.5–24.9) What it means: BMI ignores muscle — very muscular people can read high despite low fat.

Key terms

BMI:: Body Mass Index \u2014 weight (kg) divided by height (m) squared.

Common mistakes to avoid

Treating BMI as body fat \u2014 very muscular people read high despite low fat.
Using adult BMI for children/teens \u2014 they use age-and-sex percentiles.
Reading one number as a diagnosis instead of a screening guide.

Compared to alternatives

BMI vs Body Fat %

BMI is a quick height-weight screen; body-fat % measures actual composition.

	BMI	Body Fat %
Measures	Weight relative to height	Share of weight that is fat
Best for	Fast population screening	Tracking fat loss / fitness
Weakness	Misreads muscular people	Tape estimates vary ±3-4%

Bottom line: Use BMI for a quick check; use body fat % when muscle could distort BMI.

BMI calculator·Body Fat % calculator

Waist-Hip Ratio vs BMI

Fat distribution versus overall weight-for-height.

	Waist-Hip Ratio	BMI
Captures	Where fat sits	Total weight vs height
Flags	Central/visceral risk	General category
Weakness	Measurement technique	Misreads muscle

Bottom line: Use both — waist-hip ratio catches belly-fat risk BMI alone can miss.

Waist-Hip Ratio calculator·BMI calculator

Related concepts

How BMI connects to the concepts around it.

Body Fat:: The share of body weight that is fat.
BMR:: The calories your body burns at complete rest.
Ideal Weight:: A healthy target weight for your height.
Waist-Hip Ratio:: Waist divided by hip, a fat-distribution risk marker.
Body Composition:: The body's make-up of fat versus lean mass.

Health learning path

A sensible order to learn these concepts.

BMIBody FatBMRTDEECalories

Reviewed sources & methodology

Methodology: Government / Standard · Last reviewed June 2026.

World Health Organization · Government / Official
U.S. CDC · Government / Official

Keywords: bmi, health.

Sources: World Health Organization \u2014 BMI classification

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the BMI Calculator free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the BMI Calculator?+

BMI Calculator uses the standard bmi formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The BMI Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the BMI Calculator on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Calculate your Body Mass Index in seconds.

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The fastest way is to use a free in-browser bmi calculator: https://freetoolsgalaxy.com/tools/bmi-calculator. Calculate your Body Mass Index in seconds.

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Complete guide

Quick answers

What is the BMI Calculator?

How the BMI Calculator works

Component definitions

Benchmark reference

Body Mass Index

Typical values

Common interpretation errors

What impacts results most

Key assumptions

What's a typical value?

BMI categories (WHO)

Worked example

Key terms

Common mistakes to avoid

Compared to alternatives

BMI vs Body Fat %

Waist-Hip Ratio vs BMI

Related concepts

Health learning path

Reviewed sources & methodology

Frequently asked questions

Explore more

Popular tools

Explore other categories

Smart Autopilot

Likely next step

Part of a workflow

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