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BMI Calculator with Waist-to-Height Ratio
This BMI calculator gives you your body mass index, its category and the healthy weight range for your height; add your waist measurement and it also gives your waist-to-height ratio. Both are quick screening tools, not a diagnosis.
Journals that use this number
Every number calculated by code from published formulas.
- Walking plan for weight lossfrom €15Enter your current steps, height, weight, age, goal and how long you can walk. Your journal sets a weekly step ramp, picks interval or incline sessions to suit your knees and kit, and estimates the distance and energy behind every target.
- High-protein fat-loss meal planfrom €19Enter your body, activity and food preferences and get a printable journal with your calorie, protein and fibre targets, 14 days of portion-sized menus, weekly shopping lists and a 4-week habit tracker.
- GLP-1 muscle-protection planfrom €19Your journal turns your height, weight, appetite and training set-up into a daily protein number, a per-meal target and a 12-week strength plan you tick off week by week, alongside your prescriber's care.
How it's calculated
BMI is your weight in kilograms divided by your height in metres squared. The calculator uses the standard adult categories: under 18.5 is the underweight range, 18.5–24.9 the healthy range, 25–29.9 the overweight range and 30 or more the obesity range. The healthy weight range shown is the weight that would give you a BMI between 18.5 and 24.9 at your height.
BMI cannot tell muscle from fat, or show where fat is stored. That makes it misleading for some people. Athletes and people with a lot of muscle can fall in the overweight range while being lean. Older adults can have a normal BMI but low muscle and higher body fat, and a slightly higher BMI may not carry the same risk in later life. BMI categories do not apply during pregnancy, and they are not used for children, who need age-specific charts.
Risk at a given BMI also differs between ethnic groups. Some health authorities use lower thresholds for people of South Asian, Chinese, other Asian, Black African or African-Caribbean background, because health risks can rise at lower BMIs in these groups. If that applies to you, ask your doctor which thresholds are used where you live.
Waist-to-height ratio adds what BMI misses: fat around the middle, which is more closely linked to heart and metabolic risk. Divide your waist (measured at the navel) by your height, both in centimetres. Below 0.5 is generally considered lower risk, 0.5–0.6 increased risk and above 0.6 high risk. Put simply, aim to keep your waist under half your height.
Use these numbers as a prompt, not a label. If your result worries you, a doctor can look at your full picture, including blood pressure, blood tests and family history. For a closer look at body composition, try the body fat calculator; to plan a gradual change, start with the calorie calculator and an approachable routine such as the walking plan for weight loss.
| Measure | Range | Category |
|---|---|---|
| BMI | Below 18.5 | Underweight range |
| BMI | 18.5–24.9 | Healthy range |
| BMI | 25–29.9 | Overweight range |
| BMI | 30 and above | Obesity range |
| Waist-to-height ratio | Below 0.5 | Lower risk |
| Waist-to-height ratio | 0.5–0.6 | Increased risk |
| Waist-to-height ratio | Above 0.6 | High risk |
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy range. Below 18.5 is underweight, 25–29.9 overweight and 30 or more obesity. These cut-offs are population averages, so they do not fit everyone: muscular people, older adults and some ethnic groups may need a different interpretation. Pair BMI with waist size for a fuller picture.
How do I calculate BMI?
Divide your weight in kilograms by your height in metres squared. For example, 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75) = 22.9. In pounds and inches, multiply weight in pounds by 703 and divide by height in inches squared. The calculator does it instantly and shows the healthy weight range for your height.
What is a good waist-to-height ratio?
A waist-to-height ratio below 0.5 is generally considered healthy, which means keeping your waist less than half your height. Between 0.5 and 0.6 suggests increased health risk, and above 0.6 high risk. Measure your waist at the navel, relaxed, and divide by your height in the same units. It works across most adult heights and builds.
Is waist-to-height ratio better than BMI?
For estimating heart and metabolic risk, waist-to-height ratio often does better than BMI, because it reflects fat stored around the abdomen. BMI only compares weight with height. The two work best together: BMI gives a broad weight category, and waist-to-height ratio tells you whether your weight is concentrated where it matters most for health.
Is BMI accurate for athletes and muscular people?
Not very. Muscle is dense, so muscular people often get a BMI in the overweight or even obesity range while having low body fat. In that case, BMI is not a useful measure on its own. Waist-to-height ratio or a body fat estimate gives a much more realistic picture of your health and composition.
Does BMI change with age?
The formula and adult categories stay the same, but what your BMI means changes. With age, muscle tends to decrease and fat increases, so the same BMI can hide more body fat. Some research suggests a slightly higher BMI is not linked to more risk in older adults. Strength, waist size and overall health matter more than the number.
Do BMI ranges differ by ethnicity?
Yes, in some guidelines. Because health risks such as type 2 diabetes can rise at lower BMIs in certain groups, including people of South Asian, East Asian, Black African and African-Caribbean background, some health authorities use lower thresholds for them. The standard ranges in this calculator are the general adult categories, so ask your doctor what applies to you.
Other calculators
- Calorie Calculator: Your Maintenance Calories (TDEE)
- Macro Calculator: Protein, Carbs and Fat for Your Goal
- Heart Rate Zone Calculator: Find Your Zone 2 and All Five Zones
- Body Fat Calculator: US Navy Tape-Measure Method
- Water Intake Calculator: How Much Water Should You Drink?
- Protein Calculator: How Much Protein Do You Need?
General fitness information, not medical advice. Check with a doctor if you have a medical condition, are pregnant or have an injury.