BMI calculator: check your body mass index
Check your BMI and waist-to-height ratio, and what each number means.
- Kilograms and centimetres
- WHO adult categories
- Waist-to-height ratio
Quick answer
BMI (body mass index) is your weight in kilograms divided by your height in metres squared. For adults, the World Health Organization groups it like this: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity. It is a screening number, not a diagnosis.
This free calculator is from Dr. Pedro Yelamo Vera, a GP licensed in Spain (Colegiado No. 484814280) who sees adults and families by video in English and Spanish. Type your weight and height to see your BMI. Add your waist size to see your waist-to-height ratio too, which says more about fat around the middle.
Work out your BMI
For adults aged 18 and over. Nothing you type leaves your device.
Enter your weight and height to see your result.
What is a healthy BMI for adults?
For most adults a BMI of 18.5 to 24.9 is the healthy range. The same cut-offs apply to women and men. The WHO, the NHS, the US CDC and Spain's Ministry of Health all use them. The Spanish society SEEDO also splits overweight into two grades: 25 to 26.9 and 27 to 29.9.
| BMI | WHO category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 or more | Obesity (30–34.9 class 1, 35–39.9 class 2, 40+ class 3) |
Waist-to-height ratio
| Under 0.5 | No added risk from fat around the middle |
| 0.5 – 0.59 | Increased risk |
| 0.6 or more | High risk |
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres, squared. For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In Spanish it is called IMC, índice de masa corporal.
Weigh yourself in the morning, in light clothes, on a flat floor. Measure your height without shoes, standing straight against a wall.
What does BMI not tell you?
BMI does not tell fat from muscle, so athletes and very muscular people can score high with little body fat. It does not show where fat sits, and fat around the waist matters more for heart health and type 2 diabetes.
BMI also reads differently in older adults, who lose muscle with age. People of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background have a higher health risk at a lower BMI. UK NICE guidance uses 23 and 27.5 as the overweight and obesity cut-offs for them.
That is why a doctor also looks at your waist, your blood pressure, your blood sugar and cholesterol, your family history and how you feel, not just one number.
Can I use a BMI calculator in pregnancy?
No. Weight changes in pregnancy are expected, so the adult BMI ranges do not apply. Your midwife or doctor uses your weight before pregnancy to plan your care. Ask them if you have questions about weight gain.
What about BMI for children and teenagers?
Adult BMI ranges do not apply to anyone under 18. Children's BMI is read on growth charts by age and sex, as a percentile. In Spain, paediatric teams use the WHO growth standards. If you are a parent and you are worried about your child's weight or growth, ask your child's doctor or paediatrician rather than using this calculator.
What is waist-to-height ratio and how do I measure it?
Waist-to-height ratio is your waist size divided by your height, in the same units. The simple rule is to keep your waist to less than half your height, a ratio under 0.5. NICE guidance in the UK uses it alongside BMI for adults with a BMI under 35.
To measure your waist, find the point halfway between your lowest rib and the top of your hip bone. Breathe out gently and wrap the tape around your body at that level, snug but not tight.
What should I do with my result?
If your BMI is in the healthy range and your waist is under half your height, keep up the habits that help: regular activity, good sleep and a balanced diet.
If your BMI is above or below the healthy range, or your waist-to-height ratio is 0.5 or more, a check-up can help. A doctor can look at the causes, check your blood pressure and blood tests, and talk through options that suit you. Any treatment is only offered where clinically appropriate, following a genuine evaluation.
Learn more
BMI calculator: common questions
Is BMI accurate?
BMI is a useful first check for most adults, but it is not a diagnosis. It does not tell fat from muscle or show where fat sits. Waist size, blood pressure, blood tests and your history give a fuller picture.
What is a normal BMI for a woman or a man?
For adults the healthy range is 18.5 to 24.9 for both women and men. The WHO uses the same cut-offs for everyone over 18. Some ethnic groups have a higher risk at a lower BMI.
What is a good waist-to-height ratio?
Under 0.5, which means your waist is less than half your height. From 0.5 to 0.59 the risk linked to fat around the middle is increased, and from 0.6 it is high.
Does a high BMI mean I need medication?
No. BMI alone never decides treatment. A doctor looks at your whole health first. Medicines for weight are only prescribed if clinically indicated after an assessment, and many people start with other steps.
Can I use this calculator for my child?
No. Children and teenagers need age- and sex-specific growth charts (percentiles). If you are worried about your child's weight, ask your child's doctor or paediatrician.
What does the Weight Optimization consultation include?
A 30-minute video consultation with Dr. Pedro Yelamo Vera for €70: a review of your weight, your health and any test results, with a written plan. The fee covers the medical evaluation; medicines are paid at the pharmacy.
Sources
- World Health Organization (WHO): Obesity and overweight, fact sheet
- NICE guideline NG246: Identifying and assessing overweight, obesity and central adiposity
- NHS: Obesity
- MedlinePlus (US National Library of Medicine): Obesity
- Ministerio de Sanidad (Spain): WHO child growth standards
- SEEDO, Spanish Society for the Study of Obesity
Video consultations are for urgent, non-emergency care and planned check-ups. In an emergency, call 112 or go to the nearest hospital emergency department.
Want a doctor to look at your numbers with you?
Weight Optimization: a 30-minute video consultation for €70 with the same named doctor each time, in English or Spanish, with a written report. Appointments every day, 07:30–20:30 (Spain time).
Book a Weight Optimization visitSchedule Your Consultation
Select the date that suits you and arrange an appointment.
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A consultation provides assessment and guidance for urgent, non-emergency medical needs. Any next steps follow an individual medical assessment. In an emergency, call 112.
Please avoid sharing sensitive medical information on WhatsApp. Clinical details are handled securely during your consultation.
Price and booking terms
Weight Optimization: €70 · 30 minutes, per video consultation
Included
- Video consultation with Dr. Pedro Yelamo Vera
- Medical report
- Itemised invoice for your insurer
- Private electronic prescription under Spanish law, only if clinically indicated after the video assessment
Payment and cancellation
- You pay when you book. Prices are in euros and include applicable taxes.
- The fee covers the consultation only, not medicines, lab tests or scans.
- Cancel or change your appointment free of charge up to 24 hours before it starts.
- If you cancel less than 24 hours before, or do not attend, the fee is kept.
- If Dr. Yelamo cancels, or the video call fails because of a problem on his side, you get a full refund.