BMI Calculator
Free BMI calculator for adults in kg/cm, lbs/ft-in or stone. See your BMI category, healthy weight range for your height and a BMI chart.
Choose pounds with feet & inches, stone & pounds with feet & inches, or kilograms with centimeters
Only used for the Devine ideal body weight formula (male and female use different constants). It does not change BMI or the BMI categories.
Optional. Adult BMI categories apply from age 20; for ages 2 to 19 BMI is read as a percentile for age and sex (CDC)
Pounds (lbs) for Imperial · Kilograms (kg) for Metric
Imperial and stone — feet portion of your height
Imperial and stone — remaining inches (0–11)
Results
BMI Score — Normal weight
24.4
You're in the healthy weight range for your height (129–174 lbs). Maintaining is the goal.
- BMI Prime
- 0.98
- Healthy Weight Range for Your Height
- 129 – 174 lbs
- Weight vs Healthy BMI Range
- Within the healthy range
- Devine Ideal Body Weight
- 161 lbs
- Above Ideal Weight By
- 9.1 lbs
- Adult BMI Category
- Normal weight
- Ponderal Index
- 13.7 kg/m³
- Lower NHS thresholds (Asian, Black or Middle Eastern background)
- Overweight range (23 to 27.4)
- Underweight below
- 129 lbs (BMI 18.5)
- Overweight at or above
- 174 lbs (BMI 25.0)
The formula
BMI = Weight (kg) ÷ Height² (m²)
- BMI
- Body Mass Index
- Healthy Range
- Healthy Weight Range
- To Reach
- Weight to Reach a Healthy BMI
- BMI Prime
- BMI Prime
- PI
- Ponderal Index
- Ideal Weight
- Devine Formula
Worked example — Age 30 years, Weight 170, Weight — Stone 12 st, Weight — Pounds 2 lb
BMI Score — Normal weight = 24.4
How BMI Calculator Works
BMI = Weight (kg) ÷ Height² (m²)
BMI is a screening measure computed from weight and height. For adults 20 and older it places you in Underweight, Healthy weight, Overweight or Obesity. It does not measure body fat directly. In pounds and inches, BMI = 703 × pounds ÷ inches²; in kilograms and centimeters, BMI = kg ÷ (cm ÷ 100)².
- BMI
- Body Mass Index — Weight divided by height squared. The CDC calls it a screening measure that is moderately to strongly associated with other measures of body fat, not a direct measure of body fat.
- Healthy Range
- Healthy Weight Range — The weight range for your height that gives a BMI of 18.5 to 24.9, the CDC healthy weight category.
- To Reach
- Weight to Reach a Healthy BMI — How far your weight is from the nearest edge of the healthy band: up to the weight at BMI 18.5 if you are below it, down to the weight at BMI 24.9 if you are at or above 25.
- BMI Prime
- BMI Prime — Your BMI divided by 25, the lower edge of the overweight category. 1.00 or more means a BMI of 25 or higher.
- PI
- Ponderal Index — Weight in kilograms divided by height in meters cubed (kg/m³). It uses the same two measurements as BMI.
- Ideal Weight
- Devine Formula — Male: 50 kg + 2.3 kg per inch over 5 ft. Female: 45.5 kg + 2.3 kg per inch over 5 ft. A clinical reference point, not a rigid target.
Source: BMI is weight in kilograms divided by height in meters squared; the US customary version is weight (lb) ÷ height (in)² × 703. Adult categories (below 18.5 underweight, 18.5 to 24.9 healthy weight, 25.0 to 29.9 overweight, 30.0 and above obesity, split into classes 1, 2 and 3) are those published by the CDC for adults 20 and older. For ages 2 through 19 the CDC uses BMI-for-age percentiles instead. Lower thresholds for some ethnic backgrounds are from the NHS; the 2004 WHO expert consultation kept the international cut-offs and added further public health action points at 23.0 and 27.5. Devine ideal body weight: Devine BJ, Drug Intelligence & Clinical Pharmacy 1974;8:650–655 (50 kg men / 45.5 kg women + 2.3 kg per inch over 5 ft).
Worked Examples
The CDC FAQ example: an adult is 5'8" (68 in) tall and weighs 200 lb. What is the BMI in pounds and inches?
Height = 68 in (5'8") · Weight = 200 lbs
BMI = 703 × 200 ÷ 68² = 140,600 ÷ 4,624 = 30.4 — Obesity (Class 1: 30.0 to 34.9).
To reach the top of the healthy band (BMI 24.9) at 68 in, weight would be about 163.8 lb, so about 36.2 lb lower than 200 lb. The healthy range for 68 in is about 122 to 164 lb.
The NHS example: 70 kg at 1.70 m (170 cm).
Height = 170 cm · Weight = 70 kg
BMI = 70 ÷ 1.70² = 70 ÷ 2.89 = 24.2 — healthy weight (18.5 to 24.9).
The healthy range at 170 cm is 53.5 to 72.0 kg, so 70 kg is within it, about 2 kg under the top of the band.
Sam gives his weight in stone: 12 st 7 lb at 5 ft 9 in.
Height = 69 in (5'9") · Weight = 12 st 7 lb = 175 lb
BMI = 703 × 175 ÷ 69² = 25.8 — Overweight (25.0 to 29.9).
The weight at BMI 24.9 for 69 in is about 168.6 lb (12 st 1 lb), so about 6.4 lb below 175 lb. The healthy range for 69 in is about 125 to 169 lb.
Maria is 35, stands 5'5" (165 cm), and weighs 150 lbs (68 kg). She wants to know which BMI category she falls into using the imperial formula.
Height = 65 in (5'5") · Weight = 150 lbs
BMI = 703 × 150 ÷ 65² = 703 × 150 ÷ 4,225 = 24.96, which is reported as 25.0 — Overweight (25.0–29.9).
Maria sits right on the Normal/Overweight boundary: 24.96 is shown as 25.0, so she is classed as Overweight, while 1 lb lighter (149 lb → 24.8) she would be Normal. For screening purposes she is best treated as borderline — a good prompt to track the trend rather than the single reading.
David is a competitive rower: 6'1" (185 cm), 210 lbs (95 kg), with roughly 12% body fat as measured by a body-composition test. He is surprised his BMI flags him as Overweight.
Height = 1.85 m · Weight = 95 kg
BMI = 95 ÷ 1.85² = 95 ÷ 3.4225 = 27.76, shown as 27.8 — Overweight (25.0–29.9).
The CDC notes that based on BMI alone, a person with a lot of muscle may fall into the overweight or obesity category, and that other factors should be considered. A body-fat measurement or a health care provider's assessment covers what BMI cannot.
A 16-year-old is 5'4" (64 in) and weighs 120 lb. Which adult category is she in?
Age = 16 · Height = 64 in (5'4") · Weight = 120 lbs
BMI = 703 × 120 ÷ 64² = 20.6. No adult category applies.
At ages 2 through 19 the CDC reads BMI as a percentile for the same sex and age (healthy weight is the 5th to below the 85th percentile). The BMI number 20.6 is only the input to that chart; use the CDC Child and Teen BMI Calculator to get the percentile.
Understanding the Result
BMI is weight divided by height squared. The CDC describes it as a screening measure: for most people it is a reasonable indicator of whether they have too much or too little body fat, but it is not a direct measure of body fat, it cannot separate fat from muscle and bone, and it cannot show where fat is carried. The CDC says BMI should be considered with other factors, such as medical history, health behaviors, physical exam findings and lab results.
The NHS adds that muscular people may be classed as overweight or obese, and that a waist measurement may give a better picture of overall health; the WHO also lists waist circumference as another measure that can be used to identify overweight or obesity. Adults 20 and older use the same BMI categories regardless of age, sex or race (CDC). Under age 20 BMI is read as a percentile for the same sex and age, which is why this calculator shows only the BMI number if you enter an age under 20 and links to the CDC calculator.
For adults of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background the NHS uses lower thresholds (overweight 23 to 27.4, obese 27.5 or higher) because of a higher chance of health problems at a lower BMI. The 2004 WHO expert consultation found that the BMI at which risk is observed varies from 22 to 25 across Asian populations, kept the WHO cut-offs as the international classification, and identified 23.0 and 27.5 as further potential public health action points.
How to Use
- Choose Imperial (lbs, ft/in), Stone & pounds (st, lb, ft/in) or Metric (kg, cm).
- Enter your age if you like. Under 20, the result is a BMI number to compare with the CDC percentile chart, not an adult category.
- Enter your weight and height. Sex only affects the Devine ideal weight, not your BMI.
- Read your BMI, your category, the healthy weight range for your height and how far you are from it.
- Use the BMI chart below the result to see nearby heights and weights.
Quick Reference
| Underweight | BMI below 18.5 |
| Normal Weight | BMI 18.5 – 24.9 |
| Overweight | BMI 25.0 – 29.9 |
| Obese (Class I) | BMI 30.0 – 34.9 |
| Obese (Class II) | BMI 35.0 – 39.9 |
| Obese (Class III) | BMI 40.0 and above |
| 5'10" at 170 lbs | BMI ~24.4 (Normal) |
| 5'5" at 150 lbs | BMI ~25.0 (Overweight threshold) |
| Formula in pounds and inches | BMI = 703 × lb ÷ in² |
| Formula in kilograms and meters | BMI = kg ÷ m² |
| 1 stone | 14 lb = 6.350 kg |
| Children and teens (2–19) | Percentile for age and sex, not adult cut-offs |
| Healthy weight at 4'10" (147 cm) | 89 – 119 lb · 40.2 – 54.0 kg |
| Healthy weight at 5'0" (152 cm) | 95 – 127 lb · 43.0 – 57.8 kg |
| Healthy weight at 5'2" (157 cm) | 101 – 136 lb · 45.9 – 61.8 kg |
| Healthy weight at 5'4" (163 cm) | 108 – 145 lb · 48.9 – 65.8 kg |
| Healthy weight at 5'6" (168 cm) | 115 – 154 lb · 52.0 – 70.0 kg |
| Healthy weight at 5'8" (173 cm) | 122 – 164 lb · 55.2 – 74.3 kg |
| Healthy weight at 5'10" (178 cm) | 129 – 174 lb · 58.5 – 78.7 kg |
| Healthy weight at 6'0" (183 cm) | 136 – 184 lb · 61.9 – 83.3 kg |
| Healthy weight at 6'2" (188 cm) | 144 – 194 lb · 65.4 – 88.0 kg |
| Healthy weight at 6'4" (193 cm) | 152 – 205 lb · 68.9 – 92.8 kg |
Frequently Asked Questions
- What is a healthy BMI?
- For adults 20 and older the CDC calls a BMI of 18.5 to 24.9 a healthy weight. For example, at 5'10" (178 cm) that is roughly 129 to 174 lb (58.5 to 78.7 kg). Underweight is below 18.5, overweight is 25.0 to 29.9 and obesity is 30.0 or higher. A BMI in the healthy range is a screening result, not a full picture of health.
- How do I calculate BMI?
- Divide your weight in kilograms by your height in meters squared. With pounds and inches, multiply your weight in pounds by 703 and divide by your height in inches squared. The CDC example: a person 5'8" (68 in) tall weighing 200 lb has a BMI of 703 × 200 ÷ 68² = 30.4. This calculator does both conversions for you, including feet and inches, stone and pounds, and kilograms and centimeters.
- What is the BMI formula in pounds and inches (703)?
- BMI = 703 × weight (lb) ÷ height (in)². The 703 is a rounded conversion factor: converting exactly, 0.45359237 kg per lb divided by (0.0254 m per in)² is 703.07. This calculator uses the exact conversion, so very occasionally a result near a category boundary can differ in the last decimal from a hand calculation using 703.
- How do I calculate BMI in kg and cm?
- Convert centimeters to meters by dividing by 100, square that, then divide your weight in kilograms by it. Example: 70 kg at 170 cm is 70 ÷ 1.70² = 24.2, the same example the NHS uses. In this calculator choose Metric (kg, cm).
- How do I calculate BMI in feet, inches and stone?
- Turn feet and inches into total inches (5 ft 10 in = 70 in). Turn stone and pounds into pounds (1 stone = 14 lb, so 12 st 2 lb = 170 lb). Then use 703 × pounds ÷ inches². Choose "Stone & pounds" and the calculator does it for you: 12 st 2 lb at 5 ft 10 in is a BMI of 24.4.
- What is my BMI for my height and weight?
- Enter both above. A few reference points: 170 lb at 5'10" is 24.4; 150 lb at 5'5" is 25.0 (24.96 rounded); 70 kg at 175 cm is 22.9; 95 kg at 185 cm is 27.8. The chart under the calculator lists BMI for common heights and weights, and the quick reference lists the healthy weight range for each height.
- What are the BMI categories for adults?
- The CDC categories for adults 20 and older: Underweight below 18.5. Healthy weight 18.5 to 24.9. Overweight 25.0 to 29.9. Obesity 30.0 or higher, split into Class 1 (30.0 to 34.9), Class 2 (35.0 to 39.9) and Class 3, severe obesity (40.0 or higher).
- How much weight do I need to lose or gain to reach a healthy BMI?
- The result shows the distance from your current weight to the nearest edge of the healthy band for your height: the weight at BMI 24.9 if your BMI is 25 or higher, or the weight at BMI 18.5 if it is below 18.5. For example, at 5'10" (70 in) and 230 lb (BMI 33.0), the weight at BMI 24.9 is about 173.5 lb, so about 56.5 lb lower. It is arithmetic on a screening measure, not a recommended goal or timeline; speak with a health care provider about your own situation.
- Is BMI accurate?
- The CDC says that for most people BMI is a good indicator of whether they have too much or too little body fat, but it is not a direct measure of body fat. It cannot distinguish fat from muscle and bone and cannot show where fat is located. It is described as a screening measure that is not intended to diagnose disease, and it should be considered with other factors when assessing an individual's health.
- Is BMI accurate for athletes or muscular people?
- Not necessarily. The CDC says that based on BMI alone, a person with a lot of muscle may fall into the overweight or obesity category, and that health care providers should consider other factors. The NHS says the same: muscular people may be classed as overweight or obese. A DEXA scan, which the CDC names as a more precise but costly measure of body fat, or a health care provider's assessment can look at what BMI cannot.
- Is BMI different for men and women?
- For adults 20 and older the CDC uses the same BMI categories regardless of age, sex or race, and the BMI formula is the same. The sex field in this calculator only changes the Devine ideal body weight figure (50 kg versus 45.5 kg at 5 ft), never your BMI or category.
- What are the BMI cut-offs for Asian and other ethnic backgrounds?
- The NHS uses lower thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds: overweight from 23 to 27.4 and obese from 27.5, because they face a higher chance of health problems at a lower BMI. The 2004 WHO expert consultation found that observed risk varies from 22 to 25 across Asian populations, did not redefine cut-offs for each population, kept the WHO cut-offs as international classifications and identified 23.0 and 27.5 as further potential public health action points. This calculator shows the NHS lower-threshold reading as a separate line and leaves the standard category unchanged.
- What is BMI for children and teens?
- For ages 2 through 19 the CDC does not use the adult cut-offs. Children and teens are still growing, so BMI is compared with others of the same sex and age and expressed as a percentile: underweight is below the 5th percentile, healthy weight is the 5th to below the 85th, overweight is the 85th to below the 95th, and obesity is the 95th percentile or higher. This calculator does not compute percentiles. If you enter an age under 20 it shows only the BMI number and points to the CDC Child and Teen BMI Calculator.
- What are the limitations of using BMI alone?
- Per the CDC, BMI does not separate fat, muscle and bone mass and does not show what types of fat a person has or where they carry it, so it should be considered alongside other factors. The NHS says its adult tool is not for people under 18, pregnant people, anyone with an eating disorder or a condition affecting height, and that it should not be used to diagnose symptoms. Use BMI as one screening measure, not a diagnosis.
- What are BMI Prime and the ponderal index?
- BMI Prime is your BMI divided by 25, so 1.00 corresponds to a BMI of 25. The ponderal index is weight in kilograms divided by height in meters cubed (kg/m³). Both use the same weight and height as BMI.
- What is the Devine Ideal Body Weight formula?
- For males: 50 kg + 2.3 kg per inch over 5 ft. For females: 45.5 kg + 2.3 kg per inch over 5 ft. Originally used for clinical drug dosing — a reference point, not a personal target.
Common Uses
- •Screening — the CDC calls BMI a quick, inexpensive, reliable screening tool, and one measure among several of health
- •Checking where you sit against the adult categories before a conversation with a health care provider
- •Finding the weight range that matches the healthy BMI band for your height
- •Following your own BMI over time from the same measurements
- •Pediatric screening — the American Academy of Pediatrics Bright Futures recommends annual BMI assessment from age 2 using CDC growth charts (percentiles, not adult cut-offs)
Pro Tips
- →BMI is a screening tool, not a diagnosis. The NHS and WHO both point to waist measurement as a useful addition.
- →Under 20, do not use the adult category. Take the BMI number to the CDC Child and Teen BMI Calculator for the percentile.
- →If your background is South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean, also read the lower NHS thresholds line (overweight from 23, obese from 27.5).
- →Check the 703 factor: BMI in pounds and inches gives the same result as kg and meters, to within rounding.
- →Watch the trend, not the single number, and use the same scale and the same height every time.
Limitations to Know
- •BMI does not separate fat, muscle and bone mass, and it does not show where fat is carried (CDC). Muscular people may be classed as overweight or obese (NHS).
- •It is a screening measure and does not diagnose disease (CDC); the NHS says not to use its tool to diagnose any symptoms.
- •The NHS adult tool is not for people under 18, pregnant people, anyone with an eating disorder (diagnosed or suspected) or a condition that affects height. This calculator shows only the BMI number if you enter an age under 20.
- •The adult categories are the same regardless of age, sex or race (CDC), but the NHS applies lower thresholds for some ethnic backgrounds and the 2004 WHO consultation identified further action points at 23.0 and 27.5 for Asian populations.
- •Devine ideal body weight comes from a 1974 formula and is not meaningful well below 5 ft; treat it as a reference point.
Sources
- CDC - Adult BMI Categories
- CDC - Adult BMI Calculator
- CDC - About BMI
- CDC - BMI Frequently Asked Questions
- CDC - Child and Teen BMI Categories (ages 2 through 19)
- NHS - Calculate your body mass index (BMI) for adults
- NHS - Obesity
- WHO - Obesity and overweight fact sheet
- WHO Expert Consultation (2004), Appropriate body-mass index for Asian populations, The Lancet 363:157-163
Cite this calculator
TheCalcUniverse. "BMI Calculator: Kg, Lbs, Stone, Healthy Weight Range." TheCalcUniverse, 2026, https://thecalcuniverse.com/health/bmi-calculator/. Accessed October 25, 2026.
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