How does a BMI calculator work?

A bmi calculator takes your height and weight, applies the BMI formula, then maps the result to categories (like WHO for adults). It’s a quick screening tool, not a diagnosis.

What is a healthy BMI range?

For most adults, a BMI of 18.5–24.9 is considered normal in the WHO BMI chart. This bmi calculator also converts that into a healthy weight range for your height.

BMI calculator for kids: is BMI valid for children?

A bmi calculator can compute a child’s BMI number, but interpretation for ages 2–20 usually uses BMI-for-age percentiles (CDC). For pediatric decisions, use age/sex charts or a clinician.

Why does my result differ from the NHS BMI calculator?

Most differences are from rounding and unit conversion. The underlying BMI math is the same, so this bmi calculator should be very close to a bmi calculator NHS result when inputs match.

BMI Calculator

Q: How do you calculate BMI?

To calculate BMI, divide weight by height squared (metric) or use the 703 factor (US units). This bmi calculator runs the formula instantly and shows the category and healthy range.

Use metric or US units. Enter height and weight to get your BMI, WHO category, and a healthy weight range.

Height (ft/in) *

Weight (lb) *

What Is a BMI Calculator?

A BMI calculator (Body Mass Index calculator) is a fast way to estimate how your weight relates to your height using a simple ratio. When you use a bmi calculator, you get a single number (your BMI) that can be compared against common reference categories such as underweight, normal weight, overweight, and obesity. This is why a bmi calculator is widely used in general health checkups, fitness planning, and everyday “where do I stand?” questions.

This bmi calculator supports both Metric (cm/kg) and US units (ft/in, lb). It also shows a healthy weight range for your height based on the standard adult “normal” BMI range. If you are comparing tools like a bmi calculator NHS page, a bmi calculator Australia guide, or a bmi calculator mdcalc result, the core idea is the same: height and weight in, BMI out, then interpret with the right context.

How to Calculate BMI (BMI Calculation Formula)

Metric Formula

If you want to calculate BMI in metric units, use:

BMI = weight (kg) / height² (m)

US Formula

If you want to calculate BMI using US units, use:

BMI = 703 × weight (lb) / height² (in)

Many people ask “how do you calculate BMI?” or “how is BMI calculated?” A bmi calculator simply applies the BMI calculation formula for you, with the unit conversion handled automatically. If you prefer manual math, the formulas above match what you’ll find in most BMI references. For quick answers, using a bmi calculator online is the most convenient option.

BMI Chart & Categories (WHO)

A bmi calculator is most useful when you pair the number with a chart. For adults (age 20+), the World Health Organization (WHO) BMI categories are commonly used. The table below works as a quick BMI chart for interpreting your result from this bmi calculator.

Classification	BMI Range	Typical Interpretation
Underweight	< 18.5	May indicate low body mass
Normal	18.5–24.9	Typical “healthy BMI” range
Overweight	25.0–29.9	Higher weight relative to height
Obesity I	30.0–34.9	Increased health risk for many adults
Obesity II	35.0–39.9	Higher risk; medical guidance recommended
Obesity III	≥ 40.0	Very high risk; clinical support often needed

This bmi calculator follows the WHO-style adult categories shown above. Your result is a screening indicator, not a diagnosis. A clinician may consider other measures (waist circumference, blood pressure, labs, and your overall health) alongside any bmi calculator result.

BMI Calculator for Women, Men, and Children

People often search for a bmi calculator for women, a bmi calculator for men, or even “what’s my bmi calculator” tools that feel personalized. The BMI formula itself is the same for adults, but interpretation can vary with body composition, age, and ethnicity. For example, women typically carry a higher body fat percentage than men at the same BMI, and athletes can have higher BMI because muscle is denser than fat. That’s why using this bmi calculator is best as a first step, then adding context.

BMI Calculator for Kids / Children (2–20)

If you’re looking for a bmi calculator children or a bmi calculator for kids, note that pediatric guidance usually relies on BMI-for-age percentiles (CDC) rather than adult BMI categories. This page’s bmi calculator provides the BMI number, but children and teens are typically assessed against growth charts for their age and sex. If you need pediatric interpretation (including WHO bmi calculator pediatric references), consult a healthcare professional or age-based percentile charts.

How This BMI Calculator Works

Many users ask “how BMI calculator works.” This bmi calculator takes your height and weight, converts units if needed, applies the BMI formula, and then maps your value to WHO adult categories. It also estimates a healthy weight range for your height by reversing the formula across the standard “normal” BMI interval (18.5–24.9).

The result is instant and runs fully in your browser. That makes this bmi calculator online tool fast and privacy-friendly. You can re-check different scenarios (for example, a fitness goal weight) without creating an account.

Reverse BMI Calculator: Find a Target Weight

A common “reverse bmi calculator” use case is: “If I want a BMI of 22, what weight should I aim for?” While this page doesn’t expose a separate reverse form, the healthy weight range shown by this bmi calculator already answers the same question for the standard range. If you want a different target BMI, you can still use the BMI calculation formula with your height, or adjust the weight input until the bmi calculator returns your desired value.

If you’re tracking weight change, remember that BMI changes linearly with weight for a fixed height. Small weight adjustments can move you across categories, so use this bmi calculator as a guide and focus on sustainable habits.

Limitations and Best Practices

Like any bmi calculator, this tool has limitations. BMI does not directly measure body fat, and it does not capture where fat is distributed. It can be less informative for athletes, older adults, people with very high muscle mass, and certain medical conditions. Some populations also use adjusted thresholds (for example, some Asian guidelines). Treat any bmi calculator output as a screening number, then consider additional indicators if you’re making health decisions.

If your bmi calculator result falls in underweight or obesity ranges, it’s reasonable to discuss next steps with a clinician. For many people, changes to diet quality, strength training, and daily activity are more meaningful than chasing a single number.

NHS, Australia, and Other BMI Calculators

You might notice small differences between this bmi calculator and tools labeled bmi calculator nhs, bmi calculator australia, or other popular sites. Differences usually come from rounding, unit handling, and which category cutoffs are displayed. The math behind BMI is standard; this bmi calculator is designed to be clear, consistent, and easy to use across unit systems.

FAQs

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Use the bmi calculator above to check your BMI and healthy weight range in seconds. Switch between metric and US units, then click “Calculate BMI” to get your result instantly.

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