For most adults, a healthy BMI (body mass index) is 18.5 to 24.9. But that single number doesn't tell the whole story: the healthy range is lower for some ethnic groups, BMI can't tell muscle from fat, and where you carry weight matters too — which is why UK guidance now also uses your waist-to-height ratio. This guide explains all three, with the numbers that apply in the UK.
Key takeaways
- For most adults, a healthy BMI is 18.5–24.9; 25–29.9 is overweight and 30+ is obesity (NICE NG246).
- The thresholds are lower for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds — overweight from a BMI of 23 (NICE NG246).
- Whatever your BMI (if it's under 35), UK guidance says to also check your waist-to-height ratio: keep your waist to less than half your height (NICE NG246; NHS).
- In England in 2024, 66% of adults were overweight or living with obesity, and 70% had a waist-to-height ratio above 0.5 (NHS England, Health Survey for England 2024).
- BMI is a screening tool, not a diagnosis — it can't distinguish muscle from fat, and doesn't suit everyone (NHS).
The healthy BMI ranges
BMI is your weight in kilograms divided by your height in metres squared. For example, someone weighing 70kg who is 1.70m tall has a BMI of about 24.2 (NHS).
Work out your own with our BMI calculator, then read across:
| Category | Standard BMI | Lower thresholds* |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5–24.9 | 18.5–22.9 |
| Overweight | 25–29.9 | 23–27.4 |
| Obesity | 30 and above | 27.5 and above |
*Applies to people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family backgrounds. Sources: NICE NG246; NHS. The standard adult ranges are the same for men and women.
Here's roughly what the healthy range means in weight, by height (calculated from the BMI formula — for guidance, not a target):
| Height | Healthy range (BMI 18.5–24.9) |
|---|---|
| 5ft 0in (152cm) | 43.0–57.8kg (6st 11lb–9st 1lb) |
| 5ft 4in (163cm) | 48.9–65.8kg (7st 10lb–10st 5lb) |
| 5ft 8in (173cm) | 55.2–74.3kg (8st 10lb–11st 10lb) |
| 6ft 0in (183cm) | 61.9–83.3kg (9st 10lb–13st 2lb) |
Why the thresholds are lower for some ethnic groups
People from some backgrounds develop weight-related health risks, such as type 2 diabetes, at a lower BMI. NICE therefore sets lower thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds (NICE NG246).
The evidence is striking. A study of nearly 1.5 million people in England found the type 2 diabetes risk seen at a BMI of 30 in White adults occurred at a much lower BMI in other groups — around 23.9 in South Asian adults, 26.6 in Arab adults, 26.9 in Chinese adults and 28.1 in Black adults (Caleyachetty et al., 2021).
Same diabetes risk, lower BMI
Waist-to-height ratio: the number BMI misses
BMI doesn't capture where you carry weight, and fat around the middle carries the most health risk. So for adults with a BMI below 35, UK guidance says to also measure your waist-to-height ratio (NICE NG246).
The simple rule: keep your waist to less than half your height (NHS).
| Waist-to-height ratio | NICE category |
|---|---|
| 0.4 to 0.49 | Healthy central adiposity |
| 0.5 to 0.59 | Increased central adiposity |
| 0.6 or more | High central adiposity |
How to measure (NICE NG246; British Heart Foundation): find the point midway between the bottom of your ribs and the top of your hips, wrap a tape measure around it, breathe out naturally, then read the tape. Divide your waist by your height (in the same units).
Here's the half-height mark by height:
| Height | Keep waist under (0.5) |
|---|---|
| 5ft 0in (152cm) | 76cm / 30in |
| 5ft 4in (163cm) | 81cm / 32in |
| 5ft 8in (173cm) | 86cm / 34in |
| 6ft 0in (183cm) | 91cm / 36in |
Why it's worth measuring: NICE notes waist-to-height ratio helps predict risks such as type 2 diabetes, high blood pressure and cardiovascular disease, and a meta-analysis of over 300,000 adults found it was better than waist circumference or BMI alone at picking out cardiometabolic risk (Ashwell et al., 2012).
How common are raised numbers in the UK?
Very. In the Health Survey for England 2024, among adults (NHS England / NatCen, 2024):
- 30% were living with obesity
- 66% were overweight or living with obesity
- 70% had a waist-to-height ratio above 0.5
- 28% had a ratio of 0.6 or more
So if your numbers are higher than you'd like, you're far from alone — and small, sustained changes make a real difference. Occasionally weight that won't shift has a medical driver worth checking, such as an underactive thyroid; our guide to thyroid blood test results explains the test.
The limits of BMI
BMI is a useful screening tool, but it has real limits (NHS; NICE NG246):
- it can't tell muscle from fat, so very muscular people may get a "high" reading that overstates risk
- interpret it with caution in people aged 65 and over
- it isn't used the same way in pregnancy, or for under-18s (children use growth-chart centiles)
- it says nothing about where you carry weight — which is exactly why waist-to-height ratio is used alongside it
A 2025 international commission went further, recommending BMI always be checked against a waist measure or a direct measure of body fat, and distinguishing "clinical" from "preclinical" obesity — though that isn't UK policy (Rubino et al., Lancet, 2025).
What to do with your numbers
If your BMI or waist-to-height ratio is raised, there are free NHS routes as well as private support (NHS; NHS Better Health):
- see a GP if you'd like help, especially if you have a related condition such as high blood pressure or type 2 diabetes
- the free NHS Weight Loss Plan app offers a 12-week plan
- adults aged 40–74 without certain conditions are invited to a free NHS Health Check every five years, which includes BMI and waist
- a safe, sustainable rate of weight loss is about 0.5 to 1kg (1–2lb) a week (NHS)
Renvo can help. If you'd like to understand your numbers and build a realistic plan, our weight service starts with a free consultation with a GP — a proper conversation about your health and goals, not a checkout. Book a free consultation
A note on your relationship with weight
Numbers aren't the whole story, and for some people focusing on weight can be harmful. If you use food to cope with feelings, or worry you may have an eating disorder, please speak to a GP (NHS). The charity Beat runs free helplines (England 0808 801 0677; Scotland 0808 801 0432; Wales 0808 801 0433; Northern Ireland 0808 801 0434) — check current opening hours on their site.
Honest FAQs
What is a healthy BMI for a woman or a man?
For most adults of either sex, a healthy BMI is 18.5–24.9. The standard adult ranges don't differ by sex, though they're lower for some ethnic groups (NICE NG246).
Why is the healthy BMI lower for South Asian people?
Because health risks such as type 2 diabetes appear at a lower BMI. Research found the diabetes risk seen at a BMI of 30 in White adults occurred at around 23.9 in South Asian adults (Caleyachetty et al., 2021).
Is waist-to-height ratio better than BMI?
It captures something BMI misses — where you carry weight — and one large review found it better than BMI alone at flagging cardiometabolic risk. UK guidance uses both together (Ashwell et al., 2012; NICE NG246).
What is a healthy waist size?
The simple rule is to keep your waist to less than half your height. So someone 5ft 8in (173cm) tall should aim for a waist under about 86cm (34in) (NHS).
How much weight can I safely lose in a month?
A safe rate is about 0.5–1kg (1–2lb) a week, which is roughly 2–4kg (4–8lb) over a month (NHS).
This article is general information, not medical advice. Weight and waist figures by height are calculated for guidance only.
