Underweight BMI for South Asians: The Chart and Its Honest Limits
The short answer: for adults, a BMI under 18.5 counts as underweight, and that cut-off is the same for South Asians as for everyone else. It’s a screening number, though, not a diagnosis, so read it alongside your waist, your muscle and whether your weight has been falling without a reason.
Quick facts
- Underweight: BMI below 18.5 (adults 18 and over).
- Healthy range for South Asians: 18.5 to 22.9, because risk rises from 23 in Asian bodies.
- Under 18: use a growth chart (BMI-for-age), never the adult table.
- See a doctor first if: you lost weight without trying, or can’t gain despite eating well.
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People usually type “underweight BMI chart” into a phone after someone at a family gathering says “kitni patli ho gayi ho.” This guide gives the chart, shows how to measure properly at home, and is honest about what BMI can and can’t tell you. It sits in our Desi Weight Gain series.
Is being underweight a symptom? Check this first
Sometimes, yes. A low number on its own may just be your build. A number that is dropping is different.
If you have lost weight without dieting, or you eat properly and still can’t put anything on, see a doctor before trying to gain. Common causes include an overactive thyroid, undiagnosed diabetes, TB, coeliac disease, worms and other gut infections, depression and eating disorders. Each has its own fix, and extra ghee won’t reach any of them.
You’ve lost more than about 5% of your body weight in 6 to 12 months without trying (3 kg for a 60 kg person), or weight loss comes with night sweats, a cough lasting over 3 weeks, fever, heavy thirst and frequent urination, a racing heart, loose motions that won’t settle, or missed periods. A BMI under 16 in an adult, or feeling faint, needs a doctor within days, not weeks. Anyone who feels frightened of eating or of the scale deserves kind, early help too.
The underweight BMI chart for adults
BMI (body mass index) is your weight in kilograms divided by your height in metres, squared. That’s all it is, a ratio of weight to height.
| BMI | What it means |
|---|---|
| Under 16 | Severely underweight, see a doctor soon |
| 16 to 16.9 | Moderately underweight |
| 17 to 18.4 | Mildly underweight |
| 18.5 to 22.9 | Healthy range for South Asians |
| 23 to 27.4 | Overweight (Asian cut-off) |
| 27.5 and above | Obesity (Asian cut-off) |
The underweight line doesn’t move for Asians. What moves is the top. Because South Asian bodies tend to store more fat around the organs at a lower weight, the higher cut-offs start earlier, and our piece on BMI and waist size for South Asians explains that end of the chart.
Healthy weight by height, at a glance
| Height | BMI 18.5 is | BMI 22.9 is |
|---|---|---|
| 150 cm (4 ft 11) | 41.6 kg | 51.5 kg |
| 160 cm (5 ft 3) | 47.4 kg | 58.6 kg |
| 170 cm (5 ft 7) | 53.5 kg | 66.2 kg |
| 180 cm (5 ft 11) | 59.9 kg | 74.2 kg |
How to measure your BMI at home, properly
- Height: stand barefoot against a wall, heels together. Rest a hardback book flat on your head, mark the wall, and measure from the floor in centimetres.
- Weight: weigh first thing in the morning, after the toilet, before breakfast, in light clothes. Put the scale on a hard floor, never a rug.
- Do the sum: divide height in cm by 100 to get metres. Multiply it by itself. Divide your weight by that answer. Example: 50 kg and 1.65 m gives 1.65 × 1.65 = 2.72, and 50 ÷ 2.72 = 18.4. Just under the line.
- Waist: find the midpoint between your lowest rib and the top of your hip bone, breathe out gently, and wrap a tailor’s tape round without squeezing.
- Repeat: check weight once a week at the same time, not daily. One reading tells you little; a trend over four weeks tells you a lot.
What BMI gets wrong: the honest limits
BMI can’t see inside you. Two people can both sit at 19 while one carries firm muscle and the other has thin arms, a soft middle and little strength. That second picture is common in desk-bound young adults across Pakistan and India.
- Muscle: a fit cricketer or labourer can look “borderline” on paper and be perfectly healthy. Heavy muscle pushes the number up too.
- Waist: a slim BMI with a waist near 90 cm (men) or 80 cm (women) still points to fat around the organs.
- Naturally slim builds: some families are lean for generations, eat well, have energy and regular periods, and hold a steady 18 without trouble. Steady matters more than the digit.
- Older adults: after about 65, many doctors prefer a slightly higher BMI, because a small reserve helps during illness. A thin grandparent who is shrinking needs a check-up.
- Pregnancy: BMI isn’t used to judge weight during pregnancy; the midwife or doctor tracks gain instead.
A steady BMI of 18 is often just a build. A BMI that slides from 21 to 18 in a year is a question for a doctor.
Under 18? Use a growth chart, not this table
Children and teenagers are still growing, so the adult numbers don’t fit them. A doctor plots BMI against age and sex on a growth chart (BMI-for-age), and a child sitting below the 5th percentile, meaning lighter than 95 of every 100 same-age children, is treated as underweight.
The line on the chart matters more than any single dot. A child who has always tracked along a low line is often fine; one who drops across lines needs looking at. Teenagers never get a “gain diet” or powders, just family meals and a proper check. Our guide for parents of an underweight teenager walks through that visit.
Did you know?
BMI was devised in the 1830s by a Belgian mathematician, Adolphe Quetelet, who was studying populations, not diagnosing patients. It was only named “body mass index” in 1972. That history explains a lot: it’s excellent for comparing groups and much weaker for judging one person.
What to do if your BMI is under 18.5
First, rule out the medical causes above. Then, if a doctor finds nothing, gain slowly. About 0.25 to 0.5 kg a week is realistic; faster is mostly fat and water. That means a modest surplus of roughly 300 to 500 kcal a day from normal food (an extra roti with ghee, a glass of milk, a handful of peanuts), protein at every meal, and simple strength work so the gain lands as muscle, not just belly.
Our step-by-step plan, wazan barhane ka tarika, turns that into daily meals. People with diabetes, kidney disease or heart disease need their doctor or a dietitian to adjust any plan. And skip unlabelled “weight gainer” powders sold online or by hakeems, which have repeatedly been found to hide steroids.
Common questions about underweight BMI
What BMI is underweight for South Asians?
Below 18.5, the same as the global cut-off. What differs for South Asians is the upper end: overweight starts at 23 rather than 25.
Is a BMI of 18 bad?
Not always. If it’s stable, you eat well, have energy and your periods are regular, it may simply be your build. If it has fallen recently or you feel tired and weak, get a check-up.
What is a healthy weight for a 5 ft 3 woman?
At 160 cm, a BMI of 18.5 to 22.9 works out to roughly 47.4 to 58.6 kg. Waist size and strength matter as well as the number.
How do I calculate BMI without an app?
Turn height into metres, multiply it by itself, then divide your weight in kg by that result. A normal phone calculator does it in seconds.
Can I use the adult BMI chart for my 15-year-old?
No. Under 18, BMI has to be read on a growth chart for age and sex. Ask the child’s doctor to plot it and compare with earlier visits.
Is a BMI under 16 dangerous?
It’s classed as severely underweight and needs a doctor soon, because it can affect the heart, bones, hormones and immune defences. Don’t try to fix it alone at home.
Can you be underweight and still have belly fat?
Yes. Low muscle with fat stored round the middle is common, sometimes called “skinny fat.” That’s why a waist measurement adds useful information.
Does BMI count muscle?
No. It only sees total weight against height, so it can’t tell muscle from fat. A strength test, like how many chair stand-ups you can do, fills part of that gap.
Why am I underweight even though I eat a lot?
You may be eating less than it feels like, or something like thyroid, diabetes, worms or coeliac disease may be burning or wasting energy. A doctor can check with a few simple blood and stool tests.
Does being underweight affect periods?
It can. Too little body fat can make periods irregular or stop them, which also puts bones at risk. Missed periods with low weight need a doctor.
What BMI should older adults aim for?
Many doctors are comfortable with a slightly higher BMI after about 65, since a small reserve helps during illness. Ongoing weight loss in older people always deserves a check.
How long does it take to move from underweight to normal BMI?
At 0.25 to 0.5 kg a week, going from 18 to 19 at 165 cm (about 3 kg) takes around 6 to 12 weeks. Slower and steady beats fast and soft.