Free BMI Calculator UK: Body Mass Index Check Online

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

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:

Step 2 — Convert height to metres:

Step 3 — Square the height:

Step 4 — Divide weight by height squared:

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) |

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:

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:

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:

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](/body-fat-calculator) for the most complete picture of your weight health.