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How to Calculate BMI and Read Your Result
To calculate BMI, divide your weight in kilograms by your height in meters squared. In pounds and inches, multiply your weight by 703, then divide by your height in inches squared. A person who is 5 feet 6 inches and 190 pounds has a BMI of about 30.7.
That number takes seconds to get. Reading it well takes longer. This guide shows how to calculate BMI step by step, gives a chart by height, explains what the number misses, and covers how AHC providers use it during a medical intake.
Key Points
BMI is a screening number, not a diagnosis. The CDC uses the same adult categories for everyone aged 20 and over, but a 2010 review found the usual obesity cutoff misses about half of people with excess body fat. Pair your BMI with a waist or body fat measure for a fuller picture.
What Is BMI and Where Did It Come From?
Body mass index (BMI) compares your weight to your height. It gives one number that public health agencies use to sort adults into weight categories. The CDC calls it a screening measure and says it should be weighed with other health factors.
| Fact | Detail | Why it matters |
| First described | Belgian statistician Adolphe Quetelet, 1832 | Built to describe populations, not to diagnose people |
| Named BMI | Ancel Keys and colleagues, Journal of Chronic Diseases, 1972 | Tracked body fat at least as well as other ratios and depended less on height |
| Units | Kilograms per square meter (kg/m²) | The same unit for every adult |
| Current use | CDC, WHO and most clinics | A fast first screen before a fuller review |
Keys tested several weight and height ratios. Weight divided by height squared correlated well with body fat and stayed fairly independent of height, so it won. That history explains a lot. BMI was built for large groups, and it still works best there. Keep that in mind each time you calculate BMI for one person.
How to Calculate BMI Step by Step
You need two accurate numbers to calculate BMI: your height and your current weight. The steps below work for both unit systems. If you would rather skip the math, our free BMI calculator does it for you.
- Measure your height. Stand barefoot against a wall, heels together, and mark the top of your head with a flat object.
- Weigh yourself. Use the same scale in the morning, after the bathroom and before breakfast, in light clothing.
- Square your height. Multiply your height by itself, in inches or in meters.
- Divide. Divide your weight by the squared height. In pounds and inches, multiply the weight by 703 first.
- Round to one decimal. Near 25 or 30, a small change can move your category, so measure again.
Calculate BMI in pounds and inches. Here is the worked example from the opening.
| Step | Example: 5 ft 6 in, 190 lb | Result |
| Height in inches | 5 ft 6 in | 66 inches |
| Height squared | 66 × 66 | 4,356 |
| Weight × 703 | 190 × 703 | 133,570 |
| Divide | 133,570 ÷ 4,356 | BMI 30.7 |
Calculate BMI in kilograms and meters. The metric version skips the 703 step.
| Step | Example: 1.68 m, 86 kg | Result |
| Height squared | 1.68 × 1.68 | 2.82 |
| Divide | 86 ÷ 2.82 | BMI 30.5 |
The metric example is the same person, with 5 ft 6 in and 190 lb rounded to 1.68 m and 86 kg. That rounding moves the result from 30.7 to 30.5. That gap shows why rounding your inputs heavily can move a result near a category line.
Common Mistakes When You Calculate BMI
Most wrong results come from the inputs, not the math. A small slip can push a borderline number into a different category.
- Mixed units. Entering centimeters in an inches field, or pounds as kilograms, gives a result that is far off.
- Old numbers. A weight from months ago or a height from a driver’s license may no longer be accurate.
- Heavy rounding. Rounding 5 ft 5.5 in down to 5 ft 5 in raises BMI by about half a point.
- Skipping the square. Dividing weight by height once, not by height squared, is a common hand error.
- Forgetting 703. In pounds and inches, the result is meaningless without it.
If your number sits close to 25 or 30, calculate BMI a second time from fresh measurements. Use the same scale and time of day each time you check.
Adult BMI Chart by Height
The fastest way to calculate BMI without a calculator is to find your height and compare your weight with the two lines below. The weights mark where a BMI of 25 and a BMI of 30 begin, worked out from the CDC formula.
| Height | BMI 25 starts at | BMI 30 starts at |
| 4 ft 10 in | 120 lb | 144 lb |
| 5 ft 0 in | 129 lb | 154 lb |
| 5 ft 2 in | 137 lb | 165 lb |
| 5 ft 4 in | 146 lb | 175 lb |
| 5 ft 6 in | 155 lb | 186 lb |
| 5 ft 8 in | 165 lb | 198 lb |
| 5 ft 10 in | 175 lb | 210 lb |
| 6 ft 0 in | 185 lb | 222 lb |
| 6 ft 2 in | 195 lb | 234 lb |
| 6 ft 4 in | 206 lb | 247 lb |
Below the first column is the healthy or underweight range. Between the two columns is overweight. At or above the second column is the obesity range. For a wider view of weight ranges by height and age, see our healthy weight chart.
What Your BMI Number Means
Once you calculate BMI, the CDC sorts adults into four categories and splits obesity into three classes. The categories are the same regardless of age, sex or race for adults 20 and over.
| BMI | CDC category | Class |
| Under 18.5 | Underweight | None |
| 18.5 to under 25 | Healthy weight | None |
| 25 to under 30 | Overweight | None |
| 30 to under 35 | Obesity | Class 1 |
| 35 to under 40 | Obesity | Class 2 |
| 40 or higher | Obesity | Class 3, also called severe obesity |
A BMI of 30 is where obesity begins, and it often comes up in treatment criteria. Our guide to what a BMI of 30 means covers the health side of that line. For children and teens aged 2 to 19, the CDC uses BMI percentiles by age and sex instead, so these adult categories do not apply.
Why BMI Can Mislead
However carefully you calculate BMI, it cannot tell fat from muscle, and it cannot see where fat sits. A 2010 meta-analysis in the International Journal of Obesity pooled 32 samples with nearly 32,000 people. The usual obesity cutoffs were specific, but they missed about half of the people who had excess body fat.
- Muscular builds. Athletes and people who lift can read as overweight with little body fat.
- Older adults. Muscle declines with age, so a normal BMI can hide higher body fat.
- Ancestry. The American Medical Association noted in 2023 that BMI rests mainly on data from earlier generations of non-Hispanic white people.
- Asian ancestry. A 2004 WHO expert panel in The Lancet found higher health risk at lower BMIs in many Asian groups.
- Fat location. Fat around the organs carries more risk than fat under the skin, and BMI cannot see it.
The AMA policy recommends using BMI alongside other measures, such as visceral fat, body composition and waist circumference. In 2025, a Lancet Diabetes and Endocrinology commission of 56 experts went further. It advised confirming excess body fat with another measure, such as waist size or a body fat scan. The exception is a BMI of about 40 or higher.
Better Measures to Pair With BMI
After you calculate BMI, each of these fills a gap it leaves. None needs a clinic visit, and most take a tape measure and two minutes.
| Measure | What it adds | How to get it |
| Waist-to-height ratio | Shows belly fat linked to heart and metabolic risk | Waist in inches divided by height in inches |
| Body fat percentage | Separates fat from muscle | Our body fat calculator gives an estimate |
| Visceral fat estimate | Flags fat around the organs | Our visceral fat calculator gives an estimate |
| Waist circumference | A quick single number for central fat | Tape at the top of the hip bones, after a normal breath out |
NICE’s current UK obesity guideline, NG246 from 2025, keeps a rule first added in 2022. Keep your waist under half your height. It recommends the check for adults with a BMI under 35. Our guide to waist to height ratio shows how to measure it and read the result.
How AHC Providers Use Your BMI
At AHC, your BMI is a starting point for review, not a decision. Your height and weight go into the medical intake form for the treatment you choose, and every medication has its own form. An AHC provider then reviews the full picture.
| What you submit | What it shows your AHC provider | What happens next |
| Height and current weight | Your BMI and category | One input among many |
| Health history and conditions | Risks and possible reasons to wait | Shapes whether treatment fits |
| Current medications | Possible interactions | Reviewed before any approval |
If you calculate BMI at home first, enter the same height and weight on the form. Payment is made when you submit the intake. Your AHC provider can approve or decline based on your history and answers, and approval is never guaranteed. Results vary by individual and depend on adherence, clinical guidance and lifestyle factors. If you want to bring your BMI down before or alongside treatment, our guide on how to lower your BMI covers the basics.
Start with real numbers
Measure, then use the calculator, then answer the intake with the same figures. Begin your evaluation when you are ready
Frequently Asked Questions
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703. Divide that by your height in inches squared. Round to one decimal place.
What is a healthy BMI for adults?
The CDC lists 18.5 to under 25 as the healthy weight range for adults aged 20 and over. It is a screening range, not a health verdict.
Is BMI accurate for muscular people or older adults?
Less so. BMI cannot separate muscle from fat. Pair it with a waist or body fat measure for a clearer read.
Does AHC approve treatment based on BMI alone?
No. When you calculate BMI before intake, treat it as one input. Your AHC provider reviews your full intake, and approval is never guaranteed.
Where does my BMI go during the AHC intake?
You enter your height and weight on the medical intake form for the treatment you select. Your AHC provider sees the result alongside your health history.
Should I calculate BMI before starting my AHC intake?
Yes. It helps you enter accurate figures. Calculate BMI from a fresh measurement, not a remembered one, and use the same numbers on the form.
What if my weight changes after I submit my intake?
Contact AHC support through live chat on the website or at [email protected]. Share your updated weight so your AHC provider has current information.
Does AHC use insurance BMI rules?
No. AHC is cash-pay only and does not bill insurance. AHC can provide a letter of medical necessity if you want to seek reimbursement yourself.
Can I talk to an AHC provider about my BMI result?
Yes. A provider consultation costs $29.99. It is a good place to ask how to calculate BMI correctly and what your number means for you.
What happens if an AHC provider declines my order?
Contact AHC support to understand your options. Refunds, when issued, typically take 3 to 5 business days depending on your bank.
Tools to Plan Your Next Step
Two more free tools help once you calculate BMI and want a plan.
- Weight loss calculator. Set a starting point and a goal weight you can discuss with your AHC provider.
- TDEE calculator. Estimate how much energy your body uses each day at your current weight.
Have questions about your number? Speak with an AHC provider for $29.99 before you begin.
Medical Disclaimer
This content is for informational purposes only and is not medical advice. Compounded medications are prepared by state-licensed pharmacy partners. They are not FDA-approved and have not been reviewed by the FDA for safety, efficacy or quality. Prescriptions are issued by independently contracted, U.S.-licensed clinicians following an individual medical review, and approval is never guaranteed. Results vary by individual and depend on adherence, clinical guidance, and lifestyle factors. For questions about your treatment, contact AHC support through live chat on the website or at [email protected]. If you have severe symptoms, seek medical care.