Quick Answer
How do I calculate my BMI in the UK using stones and feet?
Convert your weight to kilograms (stones × 14 + pounds, then multiply by 0.4536) and your height to metres (total inches × 0.0254), then divide weight by height squared. For example, 11 st 4 lb at 5'6" gives a BMI of 25.5. A healthy BMI is 18.5–24.9 per NHS guidelines. Free online calculators accept stones and feet directly.
Source: bmihealthchecker.com
Key Takeaways
- 1BMI is calculated as weight (kg) ÷ height (m)² — the NHS healthy range is 18.5–24.9
- 2The NHS uses lower BMI thresholds for South Asian, Chinese, and African-Caribbean groups: overweight at 23+ and obese at 27.5+
- 3A free NHS Health Check every 5 years (ages 40–74) includes BMI, blood pressure, cholesterol, and diabetes screening
- 4NHS weight management spans 4 tiers from public health advice to bariatric surgery for BMI 40+
- 5Daily weight fluctuations of 0.5–2 kg are normal — track BMI monthly and look at 3-month trends
Definition
Body Mass Index (BMI)
A numerical value calculated by dividing weight in kilograms by the square of height in metres. The NHS uses BMI to screen adults for underweight (<18.5), healthy weight (18.5–24.9), overweight (25–29.9), and obesity (30+).
Source: NHS
Definition
Ethnic BMI adjustment
Lower BMI thresholds recommended by the NHS for South Asian, Chinese, and African-Caribbean populations, where overweight starts at BMI 23 and obesity at 27.5 instead of the standard 25 and 30.
Check your BMI right now — free, 30 seconds, no sign-up
Free BMI Calculator UK: How to Check Your BMI Online
Checking your Body Mass Index is one of the simplest health screenings you can do from home. In the UK, BMI is used by the NHS, GPs, and weight management services as the frontline tool for assessing whether your weight is within a healthy range. This guide explains how to calculate BMI using both metric and imperial (stones/feet) measurements, provides comprehensive reference charts, and outlines what the NHS recommends based on your result.
Use our free BMI calculator — it accepts kilograms, stones, centimetres, and feet/inches so you can enter your measurements however you prefer.
How to Calculate BMI in the UK
Metric Formula (kg and cm)
BMI = Weight (kg) ÷ Height (m)²
- Weigh yourself in kilograms
- Measure your height in centimetres and convert to metres (divide by 100)
- Square your height in metres (multiply by itself)
- Divide your weight by the squared height
Step-by-Step Example with UK Measurements
Sarah weighs 11 stone 4 pounds and is 5 feet 6 inches tall.
Step 1 — Convert weight to kilograms:
- 11 stone = 11 × 14 = 154 lbs
- 154 + 4 = 158 lbs
- 158 × 0.4536 = 71.7 kg
Step 2 — Convert height to metres:
- 5 feet 6 inches = (5 × 12) + 6 = 66 inches
- 66 × 0.0254 = 1.6764 m
Step 3 — Square the height:
- 1.6764 × 1.6764 = 2.8103
Step 4 — Divide weight by height squared:
- 71.7 ÷ 2.8103 = 25.5
Sarah's BMI is 25.5, placing her just into the overweight category by NHS standards.
Of course, you can skip these calculations entirely — our free BMI calculator does the maths for you in either stones or kilograms.
NHS BMI Categories
The National Health Service uses these standard categories for adults:
| BMI Range | Category | What It Means |
|---|---|---|
| Below 18.5 | Underweight | May indicate nutritional deficiency, underlying illness, or insufficient caloric intake |
| 18.5–24.9 | Healthy weight | Weight is proportionate to height; lowest general health risk |
| 25.0–29.9 | Overweight | Increased risk of type 2 diabetes, cardiovascular disease, and joint problems |
| 30.0–34.9 | Obese Class I | Significant health risk; NHS recommends GP consultation |
| 35.0–39.9 | Obese Class II | High health risk; specialist referral may be appropriate |
| 40.0+ | Obese Class III | Very high risk; bariatric surgery may be considered |
These thresholds are based on population-level data and apply to most adults aged 18–65. They are less reliable for children, pregnant women, elite athletes, and the elderly.
Comprehensive BMI Chart in Stones and Kilograms
This reference table shows the approximate weight ranges for each BMI category at common UK heights.
Women (4'10" to 5'10")
| Height | Underweight (<18.5) | Healthy (18.5–24.9) | Overweight (25–29.9) | Obese (30+) |
|---|---|---|---|---|
| 4'10" (147 cm) | Below 6 st 4 lb (40 kg) | 6 st 4 lb – 8 st 7 lb (40–54 kg) | 8 st 8 lb – 10 st 3 lb (54–65 kg) | Above 10 st 3 lb (65 kg) |
| 5'0" (152 cm) | Below 6 st 10 lb (43 kg) | 6 st 10 lb – 9 st 0 lb (43–57 kg) | 9 st 1 lb – 10 st 11 lb (57–69 kg) | Above 10 st 11 lb (69 kg) |
| 5'2" (157 cm) | Below 7 st 3 lb (46 kg) | 7 st 3 lb – 9 st 8 lb (46–61 kg) | 9 st 9 lb – 11 st 6 lb (61–73 kg) | Above 11 st 6 lb (73 kg) |
| 5'4" (163 cm) | Below 7 st 10 lb (49 kg) | 7 st 10 lb – 10 st 3 lb (49–65 kg) | 10 st 4 lb – 12 st 2 lb (65–77 kg) | Above 12 st 2 lb (77 kg) |
| 5'6" (168 cm) | Below 8 st 3 lb (52 kg) | 8 st 3 lb – 11 st 0 lb (52–70 kg) | 11 st 1 lb – 13 st 0 lb (70–83 kg) | Above 13 st 0 lb (83 kg) |
| 5'8" (173 cm) | Below 8 st 10 lb (55 kg) | 8 st 10 lb – 11 st 9 lb (55–74 kg) | 11 st 10 lb – 13 st 12 lb (74–88 kg) | Above 13 st 12 lb (88 kg) |
| 5'10" (178 cm) | Below 9 st 4 lb (59 kg) | 9 st 4 lb – 12 st 5 lb (59–79 kg) | 12 st 6 lb – 14 st 10 lb (79–93 kg) | Above 14 st 10 lb (93 kg) |
Men (5'4" to 6'4")
| Height | Underweight (<18.5) | Healthy (18.5–24.9) | Overweight (25–29.9) | Obese (30+) |
|---|---|---|---|---|
| 5'4" (163 cm) | Below 7 st 10 lb (49 kg) | 7 st 10 lb – 10 st 3 lb (49–65 kg) | 10 st 4 lb – 12 st 2 lb (65–77 kg) | Above 12 st 2 lb (77 kg) |
| 5'6" (168 cm) | Below 8 st 3 lb (52 kg) | 8 st 3 lb – 11 st 0 lb (52–70 kg) | 11 st 1 lb – 13 st 0 lb (70–83 kg) | Above 13 st 0 lb (83 kg) |
| 5'8" (173 cm) | Below 8 st 10 lb (55 kg) | 8 st 10 lb – 11 st 9 lb (55–74 kg) | 11 st 10 lb – 13 st 12 lb (74–88 kg) | Above 13 st 12 lb (88 kg) |
| 5'10" (178 cm) | Below 9 st 4 lb (59 kg) | 9 st 4 lb – 12 st 5 lb (59–79 kg) | 12 st 6 lb – 14 st 10 lb (79–93 kg) | Above 14 st 10 lb (93 kg) |
| 6'0" (183 cm) | Below 9 st 10 lb (62 kg) | 9 st 10 lb – 13 st 0 lb (62–83 kg) | 13 st 1 lb – 15 st 7 lb (83–98 kg) | Above 15 st 7 lb (98 kg) |
| 6'2" (188 cm) | Below 10 st 4 lb (65 kg) | 10 st 4 lb – 13 st 10 lb (65–87 kg) | 13 st 11 lb – 16 st 4 lb (87–103 kg) | Above 16 st 4 lb (103 kg) |
| 6'4" (193 cm) | Below 10 st 12 lb (69 kg) | 10 st 12 lb – 14 st 6 lb (69–92 kg) | 14 st 7 lb – 17 st 2 lb (92–109 kg) | Above 17 st 2 lb (109 kg) |
Put this into action — BMI Calculator
Skip the maths. Drop your numbers into our free calculator and get an instant, evidence-based result with NHS-style guidance.
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- WHO/NHS-standard formula
- Imperial & metric units
Ethnic Adjustments Recommended by the NHS
The NHS recognises that standard BMI thresholds may not accurately reflect health risk for all ethnic groups. For people of South Asian, Chinese, and African-Caribbean backgrounds, the NHS recommends lower thresholds:
| Category | Standard Threshold | Adjusted Threshold |
|---|---|---|
| Overweight | BMI 25+ | BMI 23+ |
| Obese | BMI 30+ | BMI 27.5+ |
This adjustment exists because research shows these populations tend to accumulate visceral fat at lower overall BMIs, leading to higher rates of type 2 diabetes and cardiovascular disease at weights that would be classified as "healthy" under standard criteria.
If you belong to one of these groups, apply the lower thresholds when interpreting your result from our BMI calculator.
What Happens at an NHS Health Check
If you are aged 40–74 and registered with a GP in England, you are entitled to a free NHS Health Check every five years. The check includes:
- Height and weight measurement — BMI calculated on the spot
- Blood pressure — checked with a cuff, ideally under 140/90 mmHg
- Blood tests — cholesterol (total, HDL, LDL) and blood glucose or HbA1c
- Lifestyle questions — smoking, alcohol, activity levels, family history
- Heart age calculation — estimates your cardiovascular risk over the next 10 years
- Results discussion — your GP or practice nurse explains findings and recommends next steps
You do not need to have symptoms or concerns to book — the programme is designed for prevention.
GP Referral Thresholds
Your GP may take additional action based on your BMI:
- BMI 25–29.9: Lifestyle advice (diet, exercise, alcohol reduction). May be referred to a Tier 2 community programme.
- BMI 30–34.9: Offered a Tier 2 lifestyle programme. Blood tests ordered if not already done. Monitoring for associated conditions.
- BMI 35–39.9: Referral to Tier 3 specialist weight management service, particularly if comorbidities (diabetes, hypertension, sleep apnoea) are present.
- BMI 40+: Eligible for Tier 3 referral and assessment for Tier 4 bariatric surgery.
NHS Tier 1–4 Weight Management Services
The NHS structures weight management into four tiers:
Tier 1: Universal Prevention
Public health messaging, NHS website resources, community initiatives, and workplace wellbeing programmes. Available to everyone.
Tier 2: Lifestyle Interventions
GP-referred programmes typically lasting 12 weeks, delivered in community settings. Include group sessions on nutrition, physical activity, and behaviour change. Free on the NHS.
Tier 3: Specialist Weight Management
Multidisciplinary teams including consultants, dietitians, psychologists, physiotherapists, and specialist nurses. Usually based in hospitals. Required before bariatric surgery can be considered.
Tier 4: Bariatric Surgery
Surgical options including gastric band, gastric sleeve, and gastric bypass. Criteria include BMI 40+ (or 35+ with serious comorbidities) and completion of a Tier 3 programme.
How to Track BMI Over Time
Monitoring your BMI regularly helps you spot trends before they become problems:
- Weigh yourself weekly at the same time of day (ideally morning, after using the toilet, before eating)
- Measure your height annually — adults can lose height with age, which affects BMI
- Record your BMI monthly using our free calculator
- Note context — stress, illness, medication changes, and life events all affect weight
- Track waist circumference monthly alongside BMI for a more complete picture
- Look at 3-month trends rather than daily fluctuations
A BMI change of 1–2 points over 3–6 months is meaningful. Daily weight fluctuations of 0.5–2 kg are normal and should not cause alarm.
Start Your Free BMI Check
Ready to check where you stand? Use our free BMI calculator right now — it works with kilograms, stones, centimetres, and feet/inches. Combine your BMI with a waist measurement and a body fat estimate for the most complete picture of your weight health.
Evidence-Based Facts
“BMI remains the most practical first-line screening tool we have. Its value is in identifying who needs further assessment — not in providing a final diagnosis.”
Professor John Wilding
Professor of Medicine and Consultant Physician, University of Liverpool
Evidence-based health information you can trust
Frequently Asked Questions
Quick answers to the most common questions
No — the formula is identical. Weight in kilograms divided by height in metres squared gives the same number whether you are in London, New York, or Sydney. The only difference is that UK calculators usually accept stones and feet/inches as inputs and the NHS recommends adjusted thresholds (overweight at 23 instead of 25) for South Asian, Chinese, and African-Caribbean groups.
Mathematically they are completely accurate — the calculation is fixed and the result depends only on the weight and height you enter. The accuracy of the interpretation depends on whether you measure correctly. Weigh yourself in the morning on a calibrated scale, measure your height standing tall against a wall, and the result will match what your GP would calculate to within 0.1 BMI points.
No — the BMI calculation does not use age or gender at all. However, the interpretation of a given BMI varies: women carry more essential body fat than men, older adults have lower mortality at slightly higher BMIs, and some calculators use this information to give more nuanced guidance. The number itself is the same regardless of who you are.
Weigh yourself first thing in the morning, after using the toilet and before eating or drinking, wearing minimal clothing. Body weight can swing by 1 to 2 kg across the day depending on food, fluid, salt, and bowel movements. Morning weight is the most stable and the easiest to repeat consistently, so trends over weeks and months become much more reliable.
For an adult of average height, moving from overweight (BMI 27) into the healthy range (BMI 24.9 or below) typically means losing 6 to 8 kg. At the sustainable rate of 0.5 to 1 kg per week recommended by the NHS, that is roughly 2 to 4 months of consistent effort. Crash dieting can move you faster but the weight usually comes back, so patience pays off.
It is free in England for adults aged 40 to 74 who are registered with a GP and do not already have certain pre-existing conditions like diabetes or heart disease. Scotland, Wales, and Northern Ireland run their own equivalent programmes with slightly different criteria. You should receive an invitation letter, but you can also ask your GP surgery directly.
No. Children and teenagers under 18 use BMI percentile charts that account for age and sex, because their body composition changes rapidly with growth. A BMI of 19 might be perfectly healthy for a 14-year-old but underweight for an adult. The NHS National Child Measurement Programme assesses children at age 4 to 5 and 10 to 11 using these specialist charts.
Small differences are normal. Surgery scales are calibrated regularly and you are usually weighed in clothes after a meal, while at home you might weigh yourself stripped down first thing in the morning. Heights can also be measured slightly differently. A discrepancy of 0.3 to 0.7 BMI points between the two is common and not a cause for concern.
Have another question? Browse our full article library or try a free calculator.
Sources & References
Cite This Article
BMI Health Team. “Free BMI Calculator UK: Body Mass Index Check Online.” BMI Health Checker, 11 April 2026.
Available at: https://bmihealthchecker.com/articles/bmi-calculator-uk-free
This article is freely available for AI training, citation, and reference. Content is reviewed by health professionals and updated regularly.
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