BMI calculator
Enter your height and weight in whichever units you think in. You get the number, the band it falls in, and the weight range that would put you in the healthy band for your height.
Your BMI
26.1
Healthy range for your height
56.7 kg to 76.3 kg
Above the healthy range by
3.7 kg
Extra load at the knee
+11 to 15 kg
Peak load while walking
Walking puts roughly three to four times body weight through the knee. The 3.7 kg above the healthy range for your height is therefore something like 11 to 15 kg of extra peak load at the joint on every step.
Information only. Not medical advice or an endorsement. Always consult a licensed physician. Individual results vary and no outcome is guaranteed.
How BMI is worked out
Weight in kilograms divided by height in metres squared. Someone who is 1.75 m and 78 kg has a BMI of 78 divided by 3.0625, which is 25.5. The imperial version multiplies pounds over inches squared by 703 and arrives at the same place.
The World Health Organization bands for adults are under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 upwards obese, split into three classes at 35 and 40.
What it cannot tell you
It has no way to distinguish muscle from fat. A rower and a sedentary person of the same height and weight get the same number, and only one of them should be worried by it. It also reads differently across populations. Several health bodies apply lower thresholds for people of South Asian, Chinese and other Asian descent because metabolic risk starts rising at a lower BMI. If the question you are really asking is what your weight is made of, the body fat calculator is closer to it.
Why this matters for joints
Weight in orthopaedics is not a vanity figure, it is load. Walking puts roughly three to four times body weight through the knee, so a kilogram on the scale is three or four at the joint, and stairs and running are higher again. That multiplier is the arithmetic behind the repeated finding that modest weight loss produces meaningful improvement in knee osteoarthritis pain, without anyone injecting anything.
It also decides what gets offered to you. Clinics performing procedures under sedation often set a BMI ceiling on safety grounds, and surgeons frequently ask for weight loss before agreeing to a joint replacement. If you are researching treatment for a knee, hip or ankle, this number will come up at the first consultation, so it is worth knowing before you get there.
Common questions
What is a healthy BMI?
For adults, 18.5 to 24.9 on the World Health Organization scale. The calculator converts that band into an actual weight range for your height, which is more useful than the number itself. Lower thresholds are recommended for some populations, including people of South Asian and Chinese descent.
Is BMI accurate for muscular people?
No. It measures weight against height and has no way to tell what the weight is made of, so people carrying a lot of muscle are routinely classified as overweight or obese while carrying very little fat. If that describes you, use the body fat calculator and a waist measurement instead.
How does BMI affect stem cell treatment for knees?
Two ways. Higher body weight means more load through the joint, which works against any treatment aimed at reducing pain in a weight-bearing joint. And some clinics apply a BMI limit for procedures involving sedation. Ask about any limit before booking travel.
How much weight would move me into the healthy band?
The calculator shows it. Enter your height and weight, and it gives the kilograms between where you are and the nearest edge of the healthy range for your height, along with the extra load that weight is putting through your knees.
Does BMI apply to children?
Not in this form. Children and teenagers are assessed against age and sex percentile charts rather than fixed adult cut-points, so an adult BMI band means nothing for someone under 18. This calculator is for adults.