BMI Calculator

Calculate adult BMI with metric or imperial measurements

Enter weight and height in one measurement system. Metric mode uses kilograms and centimeters. Imperial mode uses pounds plus feet and inches. SnakTool returns the calculated BMI and one of four adult screening categories: Underweight, Healthy weight, Overweight, or Obesity.

BMI expresses weight relative to height rather than measuring body fat directly. The same mathematical relationship is used in both unit systems; only the units and conversion factor differ.

BMI formula using kilograms and centimeters

The metric BMI formula is BMI = weight (kg) / height (m)^2. Because SnakTool accepts height in centimeters, the entered height is divided by 100 to convert it to meters before the formula is applied.

For example, at 70 kg and 175 cm, height is 1.75 m. The calculation is 70 / (1.75 × 1.75), which gives a BMI of approximately 22.86.

Input

70 kg · 175 cm

Method

70 / (1.75 × 1.75)

Result

BMI ≈ 22.86 · Healthy weight

BMI formula using pounds, feet, and inches

For imperial measurements, SnakTool first converts the entered height to total inches using feet × 12 + inches. It then calculates BMI = 703 × weight (lb) / height (in)^2.

For example, 154 lb at 5 ft 10 in gives a total height of 70 inches. The calculation 703 × 154 / (70 × 70) gives a BMI of approximately 22.10.

Input

154 lb · 5 ft 10 in

Method

703 × 154 / (70 × 70)

Result

BMI ≈ 22.10 · Healthy weight

Adult BMI categories used by the calculator

SnakTool applies the standard adult category boundaries shown below. These ranges are screening categories for adults age 20 and older, not diagnoses or direct measurements of body composition.

The category is selected from the full calculated BMI value before display rounding, so a rounded number near a boundary should not be used by itself to infer which side of the cutoff the underlying result falls on.

What happens at BMI cutoffs such as 18.5, 25, and 30

The boundaries are applied directly to the unrounded BMI. A value below 18.5 is Underweight. A value from 18.5 up to but not including 25 is Healthy weight. A value from 25 up to but not including 30 is Overweight. A value of 30 or more is Obesity.

This matters when the displayed BMI has been rounded. Two underlying values that display similarly can fall on opposite sides of a category boundary, so SnakTool determines the category before formatting the number for display.

Adult BMI categories should not be used for children and teens

The category labels in this calculator are intended for adults age 20 and older. BMI for children and teenagers is interpreted differently because growth changes with age and the result is assessed using age- and sex-specific reference data.

SnakTool's current BMI Calculator does not calculate child or teen BMI percentiles. A raw BMI number alone should therefore not be interpreted with this adult category table for someone under 20.

BMI is a screening measure, not a diagnosis

BMI is a height-and-weight calculation that can be useful as one screening measure, but the number does not diagnose a health condition. It should not be treated as a complete assessment of an individual's health.

Other information can matter when health risk is being assessed, including medical history, health behaviors, physical examination findings, laboratory results, and measures that BMI itself does not capture.

Why BMI cannot distinguish muscle from body fat

Two people can have the same height, weight, and BMI while having different body compositions. BMI does not separate fat mass from muscle or bone, so a muscular person can have a higher BMI without the number explaining how much of that weight is body fat.

BMI also does not show where body fat is distributed. Those limitations are why the calculated category should be read as a screening classification rather than a direct body-fat measurement.

Height and weight accuracy directly affect the BMI result

Because height is squared in the formula, an inaccurate height entry can noticeably change the calculated BMI. Check that kilograms are paired with centimeters in metric mode and pounds are paired with feet and inches in imperial mode.

Weight and total height must both be greater than zero. SnakTool rejects zero or negative measurements instead of returning a BMI from invalid physical inputs.

What this BMI result does not calculate

The current calculator does not calculate body-fat percentage, waist circumference, waist-to-height ratio, calorie needs, target weight, child BMI percentile, or an individualized health-risk score.

It calculates BMI from the entered height and weight and maps that value to the four adult categories implemented by the tool. Personal medical decisions require more context than this calculation provides.

References

• CDC: Adult BMI Calculator and categories
• CDC: BMI frequently asked questions