BMI Calculator (Stone, Pounds, Feet & Inches)
Use UK-style measurements to calculate your Body Mass Index instantly.
How this BMI calculator works
This tool is designed for people who prefer stone and pounds for weight and feet and inches for height. It converts your imperial values into metric units behind the scenes, then applies the standard BMI formula:
BMI = weight (kg) / [height (m)]²
Why convert first? Because BMI is an internationally standardized measure based on kilograms and meters. By converting accurately, you get the same result you would from any clinical BMI chart.
BMI categories at a glance
Adults are usually grouped into these categories:
- Below 18.5: Underweight
- 18.5 to 24.9: Healthy weight
- 25.0 to 29.9: Overweight
- 30.0 to 34.9: Obesity Class I
- 35.0 to 39.9: Obesity Class II
- 40.0 and above: Obesity Class III
Your result panel also shows a healthy weight range in stone and pounds for your current height, which makes planning easier.
Example: BMI in stone and feet
Sample values
- Weight: 12 st 3 lb
- Height: 5 ft 6 in
Entering those values into the calculator gives a BMI near the upper end of the healthy range. A small change in either weight or height can shift BMI, so always use your most recent measurements.
Tips for accurate BMI results
- Weigh yourself at the same time of day for consistency.
- Measure height without shoes, standing straight against a wall.
- Use both stone and pounds for better precision.
- Recalculate every few weeks to track trends, not daily fluctuations.
Important limitations of BMI
BMI is useful for population-level screening, but it does not directly measure body fat. Two people with the same BMI can have very different body composition.
What BMI does not show
- Muscle mass vs fat mass
- Fat distribution (for example, abdominal fat)
- Fitness level, strength, or metabolic markers
If you are very muscular, pregnant, elderly, or managing a medical condition, discuss results with a clinician. Waist circumference, blood pressure, and blood markers often provide better context.
Frequently asked questions
Is this calculator for adults or children?
This version is for adults. Children and teens should use age- and sex-specific BMI percentile charts.
Can I enter only stone and feet?
Yes. Pounds and inches are optional fields for added precision. Leaving them blank is treated as zero.
What if I enter more than 14 pounds or 12 inches?
The math still works. The calculator automatically handles totals internally and gives a correct BMI.
Bottom line
A good BMI calculator in stone and feet makes health tracking simple for UK-style measurements. Use this tool to estimate your BMI quickly, then combine it with other indicators and professional advice for a complete picture of your health.