Harris-Benedict Calculator (Basal Metabolic Rate)

How to use this Harris-Benedict calculator

What this calculator does

This calculator estimates basal metabolic rate (BMR), the energy your body would use over a day under basal conditions, from sex, age, height, and weight. It uses the original Harris-Benedict equations and then multiplies the BMR by a selected activity factor to provide an estimated total daily energy expenditure (TDEE). BMR and TDEE are predictive estimates, not direct measurements of metabolism and not individualized nutrition prescriptions. Controlled calorimetry is the measurement approach used when a direct energy-expenditure assessment is needed; the National Academies review of energy expenditure explains how resting energy expenditure is measured and what influences it.

When to use it

Use the calculator when you want a transparent baseline for comparing energy estimates, when you are learning how age and body size enter the Harris-Benedict model, when you want to see how an activity multiplier changes a basal estimate into a daily estimate, or when you need a reproducible result that can be saved in an Excel workbook. It is not designed to diagnose a metabolic condition, establish a therapeutic calorie target, or replace advice from a qualified clinician or dietitian.

How to calculate

1. The calculator opens with a ready-to-use demonstration: male, age 30, metric units, 175 cm, 70 kg, and a moderately active factor of 1.55. Its example Excel workbook is available immediately.
2. Choose Sex, enter Age, and select the Measurement system. If you switch between metric and US customary units, the current height and weight are converted for you rather than simply relabeled.
3. Enter Height and Weight as plain numbers. Use a period for decimals. A comma is accepted only as a thousands separator, so an ambiguous value such as 1,5 is rejected rather than silently reinterpreted.
4. Select an Activity level. The live panel recalculates BMR, the activity factor, and estimated TDEE without a separate Calculate button.
5. Choose Download Excel to create a workbook from the current validated values. Choose Reset to clear the demonstration and calculated state. After Reset, Excel export is disabled until every required field has a complete valid value again.

Input guide

Sex is required and selects the male or female branch of the original Harris-Benedict equation. For example, the demonstration uses Male. Changing this control changes the equation coefficients, so it can materially change BMR even when the other values stay fixed. The label refers to the sex-specific branches used by this historical predictive model; it is not a complete representation of individual physiology.

Age is required as a whole number of years from 18 through 120; 30 years is the example. Higher age reduces the predicted BMR within each equation because age is subtracted with a sex-specific coefficient. Decimal ages, scientific notation, negative values, and ages outside the supported adult range are rejected.

Measurement system is required and can be Metric (cm, kg) or US customary (in, lb). The calculation itself is performed from canonical centimetres and kilograms so changing systems does not change the underlying person. A common mistake is manually converting a value and then switching the selector too, which would convert it a second time.

Height is required. In metric mode enter 50 – 275 cm; in US customary mode enter the equivalent range in inches. The demonstration uses 175 cm. Greater height raises the estimate because the height term is added. Enter only the numeric measurement, because the unit is shown separately beside the field.

Weight is required. In metric mode enter 10 – 500 kg; in US customary mode enter the equivalent range in pounds. The example uses 70 kg. Greater weight raises the predicted BMR because the weight term is added. Do not type unit letters into the field, and do not use decimal-comma notation.

Activity level is required for the displayed TDEE. The available factors are Sedentary 1.2, Lightly active 1.375, Moderately active 1.55, Very active 1.725, Extra active 1.9, and Professional athlete 2.3. The demonstration uses Moderately active. This selection does not alter BMR; it scales BMR to the estimated TDEE. The activity categories are broad, so avoid reading small differences between them as precise measurements of daily movement.

Output guide

Basal metabolic rate (BMR) is the primary output, shown in kilocalories per day. It is driven by sex, age, height, and weight. A higher value means the equation predicts greater basal energy use, not that metabolism is medically “better” or “worse.” Estimated total daily energy expenditure (TDEE) is also shown in kilocalories per day and equals BMR multiplied by the selected factor. It is therefore sensitive to every BMR input plus Activity level. Activity factor shows the exact multiplier used for the TDEE estimate. It is dimensionless and should be interpreted as the model assumption connecting the basal and daily estimates, not as a measured personal activity score.

Worked example

For the first-open example, the male equation is BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) – (6.75 × age). Substituting 70 kg, 175 cm, and 30 years gives 66.5 + 962.5 + 875.525 – 202.5 = 1702.025 kcal/day, displayed as 1,702 kcal/day. Multiplying by the moderately active factor of 1.55 gives 2638.13875 kcal/day, displayed as 2,638 kcal/day. The underlying workbook keeps the numeric values rather than exporting only the rounded display text. For historical context, the Roza and Shizgal reevaluation of the Harris-Benedict equation discusses later work on predicting resting energy requirements.