BMI Calculator
Use this BMI Calculator to estimate Body Mass Index (BMI) from height and weight. BMI is a simple screening metric that can help you track changes over time, but it can’t directly measure body fat, muscle distribution, or overall fitness. For a fuller picture, pair BMI with your routine and other measures—like a Basal Metabolic Rate Calculator to understand energy needs—then explore more tools in Health & Fitness.
What BMI can tell you
A quick, consistent way to compare your height-to-weight ratio across time.
What BMI can’t tell you
It doesn’t separate muscle from fat and may misclassify very athletic bodies.
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Inputs stay on your device; calculations run in your browser.
Calculate your BMI
Enter your height in centimeters (80–250 cm).
Enter your weight in kilograms (20–300 kg).
Typical range: 44–660 lb. Inches should be 0–11.
We’ll convert ft/in to total inches automatically.
If under 20, clinical BMI-for-age percentiles are typically used.
Used only to tailor interpretation text (does not change BMI).
This influences guidance text, not the BMI calculation.
Clear inputs?
This will remove your current entries and hide results.
Your BMI results
Enter your details and select Calculate to see your BMI, category, healthy weight range, and a step-by-step breakdown.
Calculating…
BMI
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BMI scale
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Goal & guidance
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Safety note: This tool is for general education and tracking. If you have health concerns, consider speaking with a qualified professional.
Healthy weight range estimate
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Based on a BMI range of 18.5–24.9 for adults. Weight is rounded to 0.1 kg (metric) or 0.5 lb (US).
Step-by-step breakdown
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How this BMI Calculator works
BMI is calculated by dividing weight by height squared. The goal is consistency: the same inputs should yield the same BMI every time, so you can compare trends across weeks and months. BMI is most useful as a broad screening metric for adults, not a complete health assessment. If you want a measurement that focuses more directly on composition, compare your BMI results with a Body Fat Calculator and track how both values move together over time.
Metric formula
BMI = weightkg ÷ (heightm2)
If height is entered in centimeters: heightm = heightcm ÷ 100
- weightkg: your weight in kilograms.
- heightm: your height in meters.
- heightm2: height multiplied by itself.
US / Imperial formula
BMI = (weightlb × 703) ÷ (heightin2)
Convert ft/in to total inches: heightin = (ft × 12) + in
- weightlb: your weight in pounds.
- heightin: your height in inches.
- 703: a unit conversion constant used in the US BMI formula.
BMI categories used on this page
Category
BMI range
General interpretation
Underweight
< 18.5
May indicate insufficient mass for height; context matters.
Normal weight
18.5–24.9
Often used as a general “healthy” screening zone for adults.
Overweight
25.0–29.9
May reflect higher body mass; muscle can influence this.
Obesity (Class I–III)
≥ 30.0
Higher screening category; focus on long-term habits and guidance.
Limitations you should know
- BMI does not distinguish between fat mass and lean mass.
- Different body frames and muscle levels can shift interpretation.
- For teens and children, clinicians often use BMI-for-age percentiles.
- Short-term fluctuations can be normal; track trends rather than one-off results.
When to use a BMI Calculator
BMI is commonly used because it’s fast, repeatable, and easy to compare. It works best as a starting point—especially when you measure it the same way each time (similar clothing, consistent scale, same unit system).
- General screening: Get a quick height-to-weight ratio estimate for adults.
- Fitness tracking: Monitor BMI trends alongside training volume and recovery.
- Weight change plans: Use the healthy weight range estimate to set realistic targets.
- Clinical intake context: Understand common categories used in paperwork and checkups.
- Progress checkpoints: Re-check monthly to see direction without obsessing over daily variance.
- Consistency across units: Compare metric and US formulas correctly when traveling or switching scales.
Worked BMI examples
These examples show the same steps this BMI Calculator uses: convert units (if needed), square height, then divide.
Example 1 (Metric): 175 cm, 72 kg
- Convert height: 175 cm ÷ 100 = 1.75 m
- Square height: 1.75² = 3.0625
- Compute BMI: 72 ÷ 3.0625 = 23.51
- Rounded to 1 decimal: 23.5 → Normal weight
Example 2 (US): 5 ft 9 in, 160 lb
- Convert height: (5 × 12) + 9 = 69 in
- Square height: 69² = 4761
- Compute BMI: (160 × 703) ÷ 4761 = 23.62
- Rounded to 1 decimal: 23.6 → Normal weight
Example 3 (Metric): 165 cm, 88 kg
- Convert height: 165 cm ÷ 100 = 1.65 m
- Square height: 1.65² = 2.7225
- Compute BMI: 88 ÷ 2.7225 = 32.33
- Rounded to 1 decimal: 32.3 → Obesity (Class I)
Common BMI Calculator mistakes
- Mixing unit systems: Entering pounds into the metric field (or kg into the US field) will distort results.
- Forgetting inches: In US mode, 5 ft 9 in is not the same as 5.9 ft—use the inches field.
- Using shoes or heavy clothing: Small measurement differences can nudge BMI across a boundary.
- Overreacting to one reading: Hydration, meals, and timing can shift weight temporarily.
- Assuming BMI equals body fat: High muscle mass can raise BMI without implying poor fitness.
- Ignoring age context: For people under 20, BMI categories here are general reference only.
Quick tips for better BMI tracking
- Measure consistently: Same time of day, similar clothing, and the same scale when possible.
- Track trends: Look at 4–8 week patterns rather than daily changes.
- Pair with context: Note strength training, endurance volume, and sleep when interpreting shifts.
- Use the healthy range card: It turns BMI boundaries into a practical weight interval for your height.
- Stay realistic: Sustainable habits typically matter more than hitting a single “perfect” number.
- Use multiple metrics: Waist measurements, fitness tests, and how you feel can add clarity.
FAQ
1) What is BMI and what does it measure?
BMI stands for Body Mass Index. It uses your height and weight to estimate a height-to-weight ratio that can be compared across time. BMI does not directly measure body fat, muscle, hydration, or where weight is carried. Instead, it provides a consistent screening number that is easy to calculate and track. Many people use BMI as a starting point, then add other context like fitness level, waist measurement, or composition estimates to interpret the result more accurately.
2) Is BMI accurate for athletes or very muscular people?
BMI can be less informative for athletes or people with high lean mass. Because BMI uses total body weight, extra muscle can raise the number even when body fat is low. In those cases, the category label may feel “too high” compared to how the person performs or looks. If you train heavily, treat BMI as one data point and pair it with other measures. Many people compare BMI with strength or endurance progress and use additional tools to estimate composition.
3) What BMI range is considered “healthy” for adults?
This BMI Calculator uses 18.5–24.9 as the general “healthy” screening range for adults, which is commonly used in public health classifications. It is not a guarantee of health, and a value outside the range does not automatically indicate a problem. Your body frame, muscle level, and medical history can change what is realistic for you. The healthy weight range estimate on this page converts those BMI boundaries into a weight interval for your specific height and chosen unit system.
4) How do I switch between metric and US/Imperial units?
Use the unit toggle at the top of the calculator card to choose Metric or US/Imperial mode. In Metric mode, enter height in centimeters and weight in kilograms. In US/Imperial mode, enter height as feet and inches, then weight in pounds. The calculator applies the correct formula for each system and shows the substituted values in the breakdown. If you travel or use different scales, switching units helps keep your inputs consistent without having to do manual conversions.
5) Does age change BMI, and what if I’m under 20?
The BMI formula itself does not change based on age; it always uses height and weight. However, interpretation can change. For children and teens, clinicians typically use BMI-for-age percentiles rather than adult category cutoffs. If you enter an age under 20, this page will show an informational note and still provide the adult BMI value for general reference. If you want a broader fitness context, you can also track metrics like resting pulse using a Heart Rate Calculator.
6) Why do I see different BMI values on different websites?
Small differences usually come from rounding, unit conversions, or how height is entered. For example, using 1.75 m vs 175 cm should match, but rounding height too early can shift the result slightly. Some tools round BMI to 0 decimals, others to 1 or 2 decimals. This page shows BMI to 1 decimal by default and allows an optional 2-decimal display for more detail. The breakdown card shows intermediate steps so you can verify exactly how your value was produced.
7) What is the healthy weight range estimate and how is it calculated?
The healthy weight range estimate converts BMI boundaries into a practical weight interval for your height. For adults, this page uses BMI 18.5 (lower boundary) and 24.9 (upper boundary). In metric, it computes weight = BMI × (height in meters squared). In US mode, it computes weight = (BMI × height in inches squared) ÷ 703. The result is rounded sensibly to keep it readable: 0.1 kg in metric or 0.5 lb in US/Imperial, and the breakdown shows the steps.
8) Can BMI tell me if I’m healthy or unhealthy?
BMI alone cannot determine health status. It is a screening metric that can be useful for tracking trends and for population-level comparisons, but it doesn’t measure fitness, lab markers, strength, or diet quality. Two people can share the same BMI while having very different body composition and lifestyle patterns. Use BMI as a starting point, then look at additional signals such as activity level, waist measurements, sleep, and how you feel. If you have concerns, consult a qualified professional for personalized guidance.
9) How should I interpret BMI if I’m trying to lose weight or gain muscle?
When your goal is fat loss, BMI can help show direction over time, especially when paired with consistent weigh-ins and lifestyle notes. For lean mass gain, BMI can rise even if your waist stays stable, so interpret changes alongside strength performance and measurements. The optional Activity/Goal selector on this page tailors the “what to do next” guidance without changing BMI itself. The healthy weight range estimate can help you choose realistic milestones, but your best target depends on your body, habits, and preferences.
10) Do my inputs get stored or sent anywhere when I use this page?
No. This BMI Calculator runs locally in your browser, and the numbers you enter are used only to compute the result shown on your screen. The page does not require an account, and it does not need your name or contact information. If you copy results using the provided buttons, the copied text goes to your device clipboard so you can paste it into notes or messages. For extra privacy, you can always reset the form to clear your entries and hide results.
Accuracy, method & references
Accuracy & method
Calculations run locally in your browser. BMI is shown to 1 decimal by default, with an optional 2-decimal view. The healthy weight range is rounded to 0.1 kg in metric or 0.5 lb in US mode for readability.
Privacy-first
Your inputs remain on your device. This page does not require sign-in to calculate BMI, and it does not ask for sensitive personal details. Optional fields (age, sex, goal) only adjust messaging and do not alter the BMI formula.
Sources & references (plain text)
BMI category ranges commonly align with public health classifications such as World Health Organization (WHO) BMI categories and general educational guidance from organizations like the Centers for Disease Control and Prevention (CDC). This page is designed for general understanding and trend tracking, not medical diagnosis.
Last Updated: January 15, 2026