Free BMI Calculator
What is BMI?
Body Mass Index (BMI) is a simple ratio of your weight to your height. It gives a quick, standardised estimate of whether you're underweight, at a healthy weight, overweight, or in the obesity range. It's widely used because it needs only two easy measurements.
BMI categories (WHO)
The World Health Organization splits adult BMI into these bands. The three obesity classes exist because risk continues to rise above 30 — grouping everything over 30 together hides a lot of range.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity (class I) |
| 35.0 – 39.9 | Obesity (class II) |
| 40.0 and above | Obesity (class III) |
Healthy weight range for your height
This is usually the more useful question. The table below converts the WHO healthy band (BMI 18.5–24.9) into an actual weight range for every height from 4′10″ to 6′6″, in both kilograms and pounds. The last column shows the weight at which BMI reaches 30, the obesity threshold.
| Height | Healthy weight (kg) | Healthy weight (lb) | BMI 30 at |
|---|---|---|---|
| 4'10" (147 cm) | 40.2–54 kg | 89–119 lb | 65.1 kg (144 lb) |
| 4'11" (150 cm) | 41.5–55.9 kg | 92–123 lb | 67.4 kg (149 lb) |
| 5'0" (152 cm) | 43–57.8 kg | 95–127 lb | 69.7 kg (154 lb) |
| 5'1" (155 cm) | 44.4–59.8 kg | 98–132 lb | 72 kg (159 lb) |
| 5'2" (157 cm) | 45.9–61.8 kg | 101–136 lb | 74.4 kg (164 lb) |
| 5'3" (160 cm) | 47.4–63.8 kg | 104–141 lb | 76.8 kg (169 lb) |
| 5'4" (163 cm) | 48.9–65.8 kg | 108–145 lb | 79.3 kg (175 lb) |
| 5'5" (165 cm) | 50.4–67.9 kg | 111–150 lb | 81.8 kg (180 lb) |
| 5'6" (168 cm) | 52–70 kg | 115–154 lb | 84.3 kg (186 lb) |
| 5'7" (170 cm) | 53.6–72.1 kg | 118–159 lb | 86.9 kg (192 lb) |
| 5'8" (173 cm) | 55.2–74.3 kg | 122–164 lb | 89.5 kg (197 lb) |
| 5'9" (175 cm) | 56.8–76.5 kg | 125–169 lb | 92.1 kg (203 lb) |
| 5'10" (178 cm) | 58.5–78.7 kg | 129–174 lb | 94.8 kg (209 lb) |
| 5'11" (180 cm) | 60.2–81 kg | 133–179 lb | 97.6 kg (215 lb) |
| 6'0" (183 cm) | 61.9–83.3 kg | 136–184 lb | 100.3 kg (221 lb) |
| 6'1" (185 cm) | 63.6–85.6 kg | 140–189 lb | 103.1 kg (227 lb) |
| 6'2" (188 cm) | 65.4–88 kg | 144–194 lb | 106 kg (234 lb) |
| 6'3" (191 cm) | 67.1–90.4 kg | 148–199 lb | 108.9 kg (240 lb) |
| 6'4" (193 cm) | 68.9–92.8 kg | 152–205 lb | 111.8 kg (246 lb) |
| 6'5" (196 cm) | 70.8–95.2 kg | 156–210 lb | 114.8 kg (253 lb) |
| 6'6" (198 cm) | 72.6–97.7 kg | 160–215 lb | 117.8 kg (260 lb) |
Calculated as BMI × height², using the exact international pound (1 lb = 0.45359237 kg). Heights are rounded to the nearest centimetre for display.
How BMI is calculated
The formula is weight (kg) ÷ height (m)². For example, an 80 kg person who is 1.80 m tall has a BMI of 80 ÷ (1.80 × 1.80) ≈ 24.7 — a healthy weight. In imperial units the formula is weight (lb) ÷ height (in)² × 703. This calculator does the conversion automatically.
The limitations of BMI
BMI doesn't distinguish fat from muscle, or account for where fat is stored. A muscular athlete can have a "high" BMI while carrying little fat, and BMI can under-flag risk in people with low muscle mass. It also varies in meaning across ages and ethnic groups. Treat it as one signal, not a verdict — waist measurement and body composition add useful context.
Two specific cases where the standard bands mislead:
- Height extremes. Because BMI divides by height squared rather than cubed, it tends to read slightly high for tall people and slightly low for short people of the same build.
- Age. Adults lose muscle and gain fat with age at the same weight, so an unchanged BMI at 60 usually represents more body fat than it did at 30.
Different cut-offs for Asian populations
Cardiometabolic risk rises at a lower BMI in people of Asian descent, so a 2004 WHO expert consultation recommended additional lower action points rather than a single global threshold. Many national guidelines — including those in India, China, Japan and the UK — use something close to these:
| BMI | Risk category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 22.9 | Increasing but acceptable risk |
| 23.0 – 27.4 | Increased risk |
| 27.5 and above | High risk |
Source: WHO Expert Consultation, "Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies",The Lancet 2004;363(9403):157–163.
Two measures worth taking alongside BMI
Waist-to-height ratio
Divide your waist circumference by your height, in the same units. A ratiobelow 0.5 — keeping your waist under half your height — is the widely used rule of thumb, and it needs nothing but a tape measure. It picks up central (abdominal) fat, which BMI is blind to. Measure at the midpoint between your lowest rib and the top of your hip bone, at the end of a normal breath out.
BMI Prime
BMI Prime is simply your BMI divided by 25. A value of 1.0 puts you exactly at the top of the healthy range; 0.9 is comfortably inside it; 1.2 means you are 20% above the upper limit. It turns the raw BMI number into a "how far off am I" ratio that is easier to track over time.
What to do with your BMI
If you'd like to change your weight, the next step is knowing your calorie needs. Use the calorie calculator to get a personalised target, or thecalorie deficit calculator to plan a safe rate of weight loss. This tool provides general information and is not medical advice.
A workable order of operations:
- Find your maintenance calories with the TDEE calculator — that is the number your weight currently sits at.
- Pick a rate of change with the deficit calculator. Around 500 kcal/day below maintenance is the usual starting point, worth roughly 0.45 kg (1 lb) a week.
- Split the target into protein, carbs and fat with the macro calculator, keeping protein high enough to protect lean mass while you lose fat.
- Log what you eat in the free calorie tracker and weigh in weekly. Adjust after two or three weeks of real data rather than after a single weigh-in — normal day-to-day fluctuation is larger than a week of fat loss.
If you want to see what those calories look like as food, low-calorie foods and high-protein foods are the two lists that matter most when you are trying to lose weight without feeling hungry.
More free calculators
BMI calculator FAQ
Is this BMI calculator free?
Yes — 100% free, no account, no ads. Enter your height and weight and your BMI appears instantly.
What is a healthy BMI?
The World Health Organization considers a BMI of 18.5–24.9 to be a healthy weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is in the obesity range.
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In imperial units it is weight (lb) ÷ height (in)² × 703. This calculator handles the conversion for you in both metric and imperial.
Is BMI accurate?
BMI is a useful population-level screening tool, but it does not measure body fat directly and cannot tell muscle from fat. Very muscular people may register as "overweight" despite being lean. Use it alongside other measures, not as a diagnosis.
Does this BMI calculator work for children?
No. This uses adult categories. BMI for children and teens is interpreted differently, using age- and sex-specific percentiles — check with a pediatric provider.
What should I weigh for my height?
The healthy-weight range is whatever puts you between BMI 18.5 and 24.9. At 5'4" (163 cm) that is roughly 49–66 kg (108–146 lb); at 5'10" (178 cm) it is about 59–79 kg (130–174 lb). The table on this page lists every height from 4'10" to 6'6" in both kg and lb.
Are the BMI cut-offs the same for everyone?
No. The WHO recommends lower action points for populations of Asian descent, where cardiometabolic risk rises earlier: 23 rather than 25 for increased risk, and 27.5 rather than 30 for high risk. Muscle mass, age and body-fat distribution also shift what a given BMI means.
What is a better measure than BMI?
Waist-to-height ratio is a useful companion and needs only a tape measure: keeping your waist under half your height (a ratio below 0.5) is the common rule of thumb. Waist circumference alone, body-fat percentage and progress photos all add information BMI cannot capture.
What is BMI Prime?
BMI Prime is your BMI divided by 25 — the upper limit of the healthy range. A BMI Prime of 1.0 means you are exactly at the top of the healthy band; 1.2 means you are 20% above it. It makes "how far off am I" easier to read than the raw number.