BMI of 18 — What does it mean?
Instant answer: A BMI of 18 is classified as underweight.
Some adults are constitutionally lean and perfectly healthy at a low BMI; others are signalling a metabolic or nutritional issue. The difference matters.
Weight examples that give a BMI of 18
| Height | Weight (kg) | Weight (lbs) |
|---|---|---|
| 160 cm (5'3") | 46.1 | 102 |
| 165 cm (5'5") | 49 | 108 |
| 170 cm (5'7") | 52 | 115 |
| 175 cm (5'9") | 55.1 | 121 |
| 180 cm (5'11") | 58.3 | 129 |
| 185 cm (6'1") | 61.6 | 136 |
Practical next steps
- Prioritise protein at every meal (1.2–1.6 g per kg of body weight).
- Use calorie-dense additions like nuts, olive oil, and avocado.
- Strength-train at least twice a week to convert added calories into muscle.
- Speak to a clinician if weight loss was unintentional.
Frequently asked questions
What does a BMI of 18 mean?
A BMI of 18 falls into the underweight category as defined by the World Health Organization. Some adults are constitutionally lean and perfectly healthy at a low BMI; others are signalling a metabolic or nutritional issue. The difference matters.
Is a BMI of 18 healthy?
This BMI is outside the WHO healthy range of 18.5–24.9 and falls into the underweight category.
What weight gives a BMI of 18 at 170 cm?
At 170 cm, a BMI of 18 corresponds to roughly 52 kg.