Precision Utility
BMI Calculator
UK
Categories
NHS
Units
Metric & Imperial
Find out whether your weight is in a healthy range using the NHS Body Mass Index formula. Enter your height and weight in metric or imperial units and the calculator instantly shows your BMI, NHS category, healthy weight range for your height and how far you are from the normal band. BMI is the most widely used screening measure in UK primary care.
Your Measurements
Your Body Mass Index
26.0
Overweight
BMI Value
26.0
Category
Overweight
Healthy Range
53.5 - 72.3 kg
Weight to Lose
2.7 kg
How the BMI calculator works
Start by choosing your preferred unit system — metric (cm and kg) or imperial (feet, inches, stones and pounds). Use the sliders or type directly into the input fields to set your height and weight.
The calculator applies the standard BMI formula used by the NHS: your weight in kilograms divided by your height in metres squared. If you enter imperial units, they are converted automatically before the calculation runs.
Your result appears instantly in the dark result card. You will see your BMI number, the NHS category it falls into (underweight, normal, overweight or obese), the healthy weight range for your height and how much weight you would need to gain or lose to reach the normal band.
The colour-coded gauge bar gives a visual snapshot of where your BMI sits across the full scale. The white marker moves in real time as you adjust the sliders.
What you need to know about BMI
The NHS uses BMI as a quick screening tool to identify possible weight problems in adults. The four standard categories are:
- Underweight — BMI below 18.5
- Healthy weight — BMI 18.5 to 24.9
- Overweight — BMI 25 to 29.9
- Obese — BMI 30 or above
BMI is widely used because it is simple, fast and requires no special equipment. However, it has well-documented limitations:
- It does not distinguish between muscle mass and body fat — athletes and muscular individuals may register as overweight despite having low body fat
- It is less accurate for older adults who have lost muscle mass, pregnant women and growing children
- Ethnic-specific thresholds may apply — the NHS notes that people of South Asian, Chinese, Black African and African-Caribbean heritage face higher health risks at lower BMI values
For a more complete picture, your GP may also measure waist circumference, blood pressure, blood sugar and cholesterol. If your BMI is 30 or above, or if you have concerns about your weight at any BMI level, book an appointment with your GP to discuss next steps.
Frequently asked questions
What is BMI and how is it calculated?
BMI stands for Body Mass Index. It is calculated by dividing your weight in kilograms by your height in metres squared: weight (kg) / height (m)². It gives a simple number used to screen whether your weight falls into a healthy range.
What are the NHS BMI categories?
The NHS uses four main BMI categories for adults: underweight (below 18.5), healthy weight (18.5 to 24.9), overweight (25 to 29.9) and obese (30 or above). These thresholds apply to most adults aged 18 and over.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat, so athletes or very muscular people may have a high BMI without excess body fat. It is also less reliable for older adults, pregnant women and certain ethnic groups.
What is a healthy BMI for adults?
A healthy BMI for most adults is between 18.5 and 24.9. Maintaining a BMI within this range is associated with lower risk of type 2 diabetes, heart disease and other weight-related health conditions.
Does BMI apply differently to different ethnic groups?
Yes. Research shows that people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean heritage may have higher health risks at a lower BMI. The NHS suggests using 23 as an overweight threshold for these groups instead of 25.
Should I see a GP about my BMI?
If your BMI is outside the healthy range, especially if it is 30 or above, it is worth speaking to your GP. They can assess your overall health, consider other factors like waist circumference and family history, and recommend next steps.