BMR Calculator Widget

Add a basal metabolic rate calculator to your website. Visitors enter sex, age, height and weight and see an estimate of the calories their body uses at complete rest, with the second equation shown alongside so the difference between methods is visible.

Health & Fitness Calculator Runs in your browser Free · no ads

Customize your widget

Theme
Auto follows the visitor's light/dark setting.
Style
Attribution on your page
Optional and entirely your choice. The exact line is shown in the code below; it links to the tool with rel="nofollow".
More options
Starting values
Leave blank to use the widget's defaults. Visitors can still change every value.

Live preview

Exactly what your visitors will see

Embed code

<iframe src="https://a2z.tools/embed/w/bmr-calculator" title="BMR Calculator by A2Z Tools" width="100%" height="630" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

Works with

How it works

Mifflin-St Jeor (1990) is the default because it is the equation the A2Z BMR and TDEE calculators use, and a 2005 systematic review of resting-metabolic-rate equations (Frankenfield and colleagues) found it the most reliable of the common ones for healthy adults. The revised Harris-Benedict equation (Roza and Shizgal, 1984) can be chosen instead. Whichever is selected, the other is shown in a second row, which makes the typical 50-100 kcal disagreement between equations obvious. Results are rounded to whole kilocalories and an hourly figure is shown. Both equations were fitted on adults, so ages under 18 get a clear message rather than a number.

Calculation method

  • Mifflin-St Jeor: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5 for men, - 161 for women
  • Harris-Benedict revised by Roza & Shizgal (1984), men: 88.362 + 13.397 x kg + 4.799 x cm - 5.677 x age
  • Harris-Benedict revised, women: 447.593 + 9.247 x kg + 3.098 x cm - 4.330 x age
  • Imperial inputs converted with 1 lb = 0.45359237 kg and 1 in = 2.54 cm; results rounded to whole kcal/day; per hour = BMR / 24

Worked examples

Woman, metric

Inputs: Female, 30 years, 165 cm, 60 kg, Mifflin-St Jeor

Result: 1,320 kcal/day; Harris-Benedict gives 1,384 kcal/day; 55 kcal per hour

600 + 1,031.25 - 150 - 161 = 1,320.25. Revised Harris-Benedict: 447.593 + 554.82 + 511.17 - 129.9 = 1,383.7.

An estimate for general information only - not medical advice. Talk to a doctor or registered dietitian about your health.

Limitations

  • Predicts resting energy for healthy adults; illness, fever, recent weight loss, thyroid conditions and some medicines change it in ways the equations do not see.
  • Uses total body weight, so very muscular or very lean people may be underestimated; the equations have no body-composition input.
  • Not for anyone under 18 or during pregnancy or breastfeeding, when needs rise.

Where publishers use it

  • Dietitians and nutrition coaches explaining resting energy before setting calorie targets
  • Fitness blogs comparing the common BMR equations with the reader's own numbers
  • Weight-management programmes that start clients with a resting-energy estimate
  • Physiology and sports-science teaching material

Questions

What is the difference between BMR and daily calories?

BMR is the energy used at complete rest. Everyday movement and exercise add to it; multiplying BMR by an activity factor gives total daily energy expenditure, which the calorie calculator widget does.

Which equation is more accurate?

In the 2005 Frankenfield systematic review Mifflin-St Jeor predicted measured resting metabolic rate within 10% for more healthy non-obese and obese adults than the other equations tested, which is why it is the default. Any equation can still be 10% or more away from an individual's measured BMR.

Why is there no result for under-18s?

Both equations were developed from adult data. Children and teenagers have growth needs that these equations do not model, so the widget asks for an age of 18 or over.

Can I preset the equation?

Yes. Use v_formula=harris in the embed URL to open with Harris-Benedict selected.

Sources

  1. A new predictive equation for resting energy expenditure in healthy individuals (Mifflin, St Jeor et al.) - American Journal of Clinical Nutrition 51(2):241-247, 1990 . Mifflin-St Jeor equation
  2. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass (Roza & Shizgal) - American Journal of Clinical Nutrition 40(1):168-182, 1984 . Revised Harris-Benedict coefficients
  3. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review (Frankenfield, Roth-Yousey, Compher) - Journal of the American Dietetic Association 105(5):775-789, 2005 . Basis for choosing Mifflin-St Jeor as the default

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools BMR Calculator
https://a2z.tools/bmr-calculator

Related widgets

More Health & Fitness widgets →

Preview

CustomizeGet code