BMR Calculator

BMR: Basal metabolic rate. This is the energy your body uses per day at complete rest, usually shown here as Estimated BMR in kcal/day and kJ/day.

Estimated BMR: Your predicted calorie burn per day at rest, not your full daily calorie needs.

Primary formula used: The equation that produced the main BMR result. Different equations can give slightly different estimates.

Mifflin-St Jeor: A common adult prediction equation that uses sex, age, height, and weight [3].

Revised Harris-Benedict: Another adult prediction equation used here for comparison or as your chosen default formula [3].

Body fat (%): The percent of your total body weight that is fat. If you enter this, the calculator can estimate lean mass.

Estimated fat-free mass: Your body weight minus estimated fat mass, shown in kg. It is the lean-mass value needed for Cunningham.

Cunningham estimate: A BMR estimate based on fat-free mass instead of total body weight [2].

kcal/day and kJ/day: Two ways to express daily energy use. kcal is common on food labels, while kJ is another energy unit.

Mistake: Entering centimeters while Unit system is set to US, or pounds while Metric is selected.
Fix: Match your entries to the visible fields only: use Height (feet) , Height (inches) , and Weight (lb) for US, or Height (cm) and Weight (kg) for Metric.

Mistake: Putting 14 into Height (inches) instead of carrying full feet into Height (feet) .
Fix: Keep Height (inches) from 0 to 11. For example, enter 6 feet 2 inches as 6 in Height (feet) and 2 in Height (inches) .

Mistake: Treating Estimated BMR like maintenance calories for a normal day.
Fix: Read Estimated BMR as calories at complete rest. Daily living and exercise usually make real daily needs higher than this result.

Mistake: Typing an impossible or mixed-up value into Body fat (%) , such as 0, 100, or a decimal that should have been a percent.
Fix: Enter Body fat (%) only if you know it, and use a percent between 0 and 100, such as 25 for 25%.

Mistake: Expecting Cunningham estimate to appear when Body fat (%) is blank.
Fix: Enter a valid Body fat (%) so the calculator can first estimate Estimated fat-free mass , which Cunningham needs.

Mistake: Comparing formulas without noticing which one drives the main answer.
Fix: Check Primary formula used . That tells you which equation produced the main Estimated BMR .

• These are prediction equations, not direct lab measurements, so your real resting energy use can be higher or lower.
• The calculator is built around adult equations. It will still calculate for younger ages, but results may be less accurate for children and teens.
• BMR is not the same as total daily energy needs. Normal activity, exercise, digestion, illness, and environment usually raise total energy use above BMR.
• If Body fat (%) is entered, the Cunningham result depends on that value being reasonably accurate. A bad body-fat estimate can make the lean-mass result less useful.
• Different formulas use different inputs and coefficients, so side-by-side estimates may not match exactly. That difference is normal.
• US entries must use inches from 0 to 11 in Height (inches). Larger inch values should be carried into Height (feet).
• The calculator requires positive age, height, and weight values and does not calculate from blank or invalid required fields.

How the calculator works

The calculator first converts US measurements to metric when needed, then computes BMR with the selected default equation. If you turn on formula comparison, it also shows the other common equation and adds Cunningham only when Body fat (%) is entered and valid.

Main formulas

weight_kg = weight_lb x 0.45359237

height_cm = (height_ft x 12 + height_in) x 2.54

Male Mifflin-St Jeor: BMR = 10 x weight_kg + 6.25 x height_cm - 5 x age_years + 5

Female Mifflin-St Jeor: BMR = 10 x weight_kg + 6.25 x height_cm - 5 x age_years - 161

Male Revised Harris-Benedict: BMR = 88.362 + 13.397 x weight_kg + 4.799 x height_cm - 5.677 x age_years

Female Revised Harris-Benedict: BMR = 447.593 + 9.247 x weight_kg + 3.098 x height_cm - 4.330 x age_years

ffm_kg = weight_kg x (1 - body_fat_pct/100)

Cunningham: BMR = 500 + 22 x ffm_kg

BMR_kj_day = BMR_kcal_day x 4.184

When each formula is used

Mifflin-St Jeor is the usual default for general adult use because it uses the standard inputs most people know: sex, age, height, and weight [3]. Revised Harris-Benedict is available as an alternate default and as a comparison estimate [3]. Cunningham is shown only when body fat is provided because it needs fat-free mass [1].

Mini example

Suppose a female user is age 30, height 5 feet 6 inches, and weight 150 lb with Mifflin-St Jeor selected.

weight_kg = 150 x 0.45359237 = 68.0388555

height_cm = (5 x 12 + 6) x 2.54 = 167.64

BMR = 10 x 68.0388555 + 6.25 x 167.64 - 5 x 30 - 161 = 1407.17625 kcal/day

BMR_kj_day = 1407.17625 x 4.184 = 5888.42543 kJ/day

This means the predicted energy use at complete rest is about 1,407 kcal/day. Real daily calorie needs are usually higher because most people are not resting all day.

Assumptions behind the estimate

These equations estimate resting energy use from body size, age, and sex, and sometimes fat-free mass. They do not directly measure hormones, illness, temperature, medications, or true lab-tested metabolic rate. That is why equation choice and body-fat accuracy can change the result.