Caloric Requirement Converter
Calculate your daily caloric requirements and convert between kcal, kJ, and per-hour rates. Uses the Mifflin-St Jeor equation with activity multipliers.
Caloric Requirement Converter
Calculator
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Formula: BMR(male) = 10w + 6.25h - 5a + 5 | BMR(female) = 10w + 6.25h - 5a - 161 | TDEE = BMR x Activity Factor
Worked example โ TDEE = 2,797.75 kcal/day (11,706.18 kJ/day)
Formula
BMR(male) = 10w + 6.25h - 5a + 5 | BMR(female) = 10w + 6.25h - 5a - 161 | TDEE = BMR x Activity Factor
The Mifflin-St Jeor equation estimates Basal Metabolic Rate from weight (kg), height (cm), age (years), and gender. TDEE multiplies BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active). Results can be converted between kilocalories and kilojoules using the factor 4.184.
Worked Examples
Example 1: Active Male Caloric Needs
Problem:Calculate daily calories for a 25-year-old male, 80 kg, 180 cm, moderately active.
Solution:BMR = 10(80) + 6.25(180) - 5(25) + 5 = 800 + 1125 - 125 + 5 = 1,805 kcal TDEE = 1,805 x 1.55 = 2,797.75 kcal/day In kJ: 2,797.75 x 4.184 = 11,706.18 kJ/day
Result:TDEE = 2,797.75 kcal/day (11,706.18 kJ/day)
Example 2: Sedentary Female Weight Loss
Problem:Calculate calories for a 40-year-old female, 65 kg, 165 cm, sedentary, with a 500 kcal deficit.
Solution:BMR = 10(65) + 6.25(165) - 5(40) - 161 = 650 + 1031.25 - 200 - 161 = 1,320.25 kcal TDEE = 1,320.25 x 1.2 = 1,584.30 kcal/day Weight loss target: 1,584.30 - 500 = 1,084.30 kcal/day
Result:TDEE = 1,584.30 kcal/day, weight loss target = 1,084.30 kcal/day
Frequently Asked Questions
How are daily caloric requirements calculated?
Daily caloric requirements are estimated using the Mifflin-St Jeor equation, which calculates your Basal Metabolic Rate (BMR) based on weight, height, age, and gender. The BMR is then multiplied by an activity factor to determine Total Daily Energy Expenditure (TDEE). For males the formula is BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 5, and for females it subtracts 161 instead of adding 5. This method is considered the most accurate non-laboratory estimation by the Academy of Nutrition and Dietetics.
What is the difference between calories and kilocalories?
In nutrition, when people say "calories" they almost always mean kilocalories (kcal). One kilocalorie equals 1,000 small calories and represents the energy needed to raise 1 kilogram of water by 1 degree Celsius. In the metric system, energy is often expressed in kilojoules (kJ), where 1 kcal equals 4.184 kJ. Food labels in the US list kilocalories as "Calories" with a capital C, while European labels typically show both kcal and kJ.
How does activity level affect caloric needs?
Activity level is applied as a multiplier to your BMR. Sedentary individuals (little or no exercise) use a factor of 1.2, while extremely active people (hard exercise 6-7 days per week plus physical job) use a factor of 1.9. A lightly active person who exercises 1-3 days per week uses 1.375, moderately active 3-5 days uses 1.55, and very active 6-7 days uses 1.725. This means a sedentary person might need 1,800 kcal per day while the same person with heavy exercise could need over 2,800 kcal.
How many calories should I eat to lose weight?
A safe rate of weight loss is 0.5 to 1 kg per week, which requires a daily deficit of 500 to 1,000 kcal below your TDEE. A mild deficit of 250 kcal per day leads to about 0.25 kg loss per week. It is generally not recommended to eat fewer than 1,200 kcal per day for women or 1,500 kcal for men without medical supervision, as this can cause nutrient deficiencies and metabolic slowdown.
What is the difference between BMR and resting metabolic rate?
Basal metabolic rate is measured under strict laboratory conditions: after an overnight fast, at complete rest, in a thermoneutral room, before any activity. Resting metabolic rate is measured with those conditions relaxed, so it typically comes out a few percent higher because digestion and residual muscle tone are still contributing. Predictive equations such as Mifflin-St Jeor were fitted to indirect calorimetry data, so the number this converter labels BMR is really a resting-rate estimate. Treat it as a baseline for the activity multiplier, not a measured physiological constant.
How does Mifflin-St Jeor compare with Harris-Benedict and Katch-McArdle?
All three predict resting energy expenditure but use different inputs. Harris-Benedict, the oldest, uses the same weight, height, age and sex variables with different coefficients and tends to read high in people carrying more fat mass. Mifflin-St Jeor was refitted on a more modern population and is the version used here. Katch-McArdle skips sex entirely and works from lean body mass, BMR = 370 + 21.6 x LBM in kilograms, so it needs a body-fat measurement but describes very lean or very muscular people better than any weight-only formula.
Why is the kilojoule figure exactly 4.184 times the kilocalorie figure?
The thermochemical calorie is defined as exactly 4.184 joules, so one kilocalorie is exactly 4.184 kilojoules and the conversion is a fixed definition rather than a measurement. A 2,000 kcal per day requirement is therefore 8,368 kJ per day. To go the other way, divide kilojoules by 4.184. Small discrepancies against packaged food labels come from rounding: manufacturers usually round both the kcal and kJ figures independently, so back-converting a label rarely reproduces the printed number to the last digit.
What does the calories-per-hour figure actually represent?
It is simply your total daily energy expenditure divided by 24, a flat average that spreads the whole day evenly across the clock. Real expenditure is nothing like flat: it falls below the resting rate during deep sleep and can rise several-fold during hard exercise. Use the per-hour value to sanity-check daily totals or to compare two profiles, not as a burn rate for a workout. For a single session, an activity-specific MET value multiplied by body mass and duration is the appropriate estimate.
When should I recalculate my requirement as my weight changes?
The weight term carries a coefficient of 10, so each kilogram gained or lost moves the resting estimate by 10 kcal per day and moves total daily expenditure by 10 multiplied by your activity factor. Losing 5 kg at a moderately active factor of 1.55 therefore reduces the estimate by about 78 kcal per day, enough to stall a small deficit. Recalculating after every 3 to 5 kg of change, or whenever your training volume shifts you into a different activity band, keeps the target honest.
Does the activity multiplier already account for the thermic effect of food?
Yes. Total daily energy expenditure has four components: resting metabolism, the thermic effect of food, deliberate exercise, and non-exercise activity thermogenesis such as fidgeting, standing and walking around. Digestion alone accounts for roughly a tenth of energy intake for a mixed diet. The activity factors from 1.2 to 1.9 were derived to bundle digestion, exercise and incidental movement together into one number, so adding a separate allowance for the thermic effect on top would double-count it and inflate your target.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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