BMR Calculator
Calculate your adult BMR with Mifflin-St Jeor, revised Harris-Benedict, or Katch-McArdle and compare resting-energy estimates, formulas, and units.
Enter your measurements and compare BMR equations
BMR calculator inputs
Estimated BMR1,760Calories/day · Mifflin-St Jeor
Formula comparison
Every row uses the same measurements.
| Equation | Estimated BMR | Difference from selected |
|---|---|---|
| Mifflin-St Jeor | 1,760 Calories/day | 0 |
| Revised Harris-Benedict | 1,835 Calories/day | 75 |
| Katch-McArdle | 1,742 Calories/day | -18 |
BMR formula comparison
The same entries evaluated with three published equations.
Resting energy by time span
The selected daily estimate shown at shorter time intervals.
Adult educational estimate only. BMR is not TDEE, a daily calorie target, or a measured metabolic rate. Do not use this calculator for children, pregnancy, breastfeeding, illness, eating-disorder care, or medical nutrition therapy.
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What does the BMR Calculator calculate?
The BMR Calculator converts the values you enter into a structured estimate using the formulas and assumptions documented on this page. Use the result to compare scenarios, review the calculation details, and identify sensitive inputs. Check the guide and formula sections before using the estimate for an important decision.
At a Glance
- Estimate adult basal metabolic rate with three published equations.
- Compare Mifflin-St Jeor, revised Harris-Benedict, and Katch-McArdle.
- See resting energy per day, hour, and week.
- Compare formula spread and estimated lean body mass.
- Use U.S. customary or metric measurements and Calories or kilojoules.
- Treat the result as a resting-energy estimate, not a total daily calorie target.
History of Basal Metabolic Rate Estimation
Basal and resting energy equations were developed because measuring energy expenditure with indirect calorimetry requires specialized equipment and controlled conditions. Harris and Benedict published influential equations in the early twentieth century. Roza and Shizgal later reevaluated the data and published revised coefficients in 1984.
Mifflin and colleagues published another adult resting-energy equation in 1990 using measured data from 498 adults. Katch-McArdle takes a different approach by estimating resting energy from lean body mass.
What This BMR Calculator Does
The calculator converts height and weight to metric units, calculates all three supported estimates, and makes the selected equation the headline result. It also converts the selected daily estimate to kilojoules, energy per hour, and energy per week. Review the BMR Calculator assumptions before relying on this result for decisions.
The formula comparison and spread metric show how much the equations disagree for the same inputs. Estimated lean body mass is derived from weight and the entered body-fat percentage.
Who Should Use It
For “Who Should Use It,” the BMR Calculator organizes the relevant inputs, applies the documented method, and shows a result that can be compared across scenarios. The points below identify the specific considerations and assumptions users should review before relying on the estimate.
- Adults seeking a transparent starting estimate of resting energy needs.
- People comparing several published BMR equations.
- Students learning how age, height, weight, sex terms, and lean mass affect energy equations.
- Adults who need a resting-energy input before using an activity-based TDEE calculator.
The calculator is not designed for children, pregnancy, breastfeeding, illness, eating-disorder care, or medical nutrition therapy.
Problems It Solves
- Converts pounds, feet, and inches to kilograms and centimeters.
- Calculates three BMR estimates from one consistent measurement set.
- Shows the exact difference between each formula and the selected method.
- Converts daily energy to hourly, weekly, and kilojoule values.
- Shows how the body-fat input affects lean mass and Katch-McArdle.
- Separates resting energy from activity-adjusted maintenance calories.
Key Benefits
All personal inputs are visible and editable. Formula constants come from the published equations, while the same tested engine powers the webpage, examples, widget, and PDF report. The comparison table and charts keep model uncertainty visible.
BMR Calculator Definitions
- BMR
- Basal metabolic rate, the estimated energy used at rest to support essential functions.
- REE
- Resting energy expenditure. Research papers often use REE for measured or estimated resting energy.
- Indirect calorimetry
- A measurement approach that estimates energy expenditure from respiratory gas exchange under a defined protocol.
- Lean body mass
- Body weight minus estimated fat mass. It includes muscle, water, bone, organs, and other non-fat tissue.
- Formula spread
- The highest BMR estimate minus the lowest for the same inputs.
- TDEE
- Total daily energy expenditure, which includes activity and other daily energy use beyond BMR.
Three BMR Estimation Methods
Mifflin-St Jeor
The default equation uses weight, height, age, and the published male or female constant. It was derived from measured resting energy expenditure in healthy adults.
Revised Harris-Benedict
The revised equations use the same general predictors with different sex-specific coefficients. Their result can differ from Mifflin-St Jeor even with identical measurements.
Katch-McArdle
This method uses estimated lean body mass rather than age and height. An inaccurate body-fat percentage directly changes estimated lean mass and BMR.
BMR vs TDEE
BMR estimates resting energy. TDEE estimates total daily energy after activity and movement are included. BMR is therefore not the same as a maintenance-calorie target.
Use the TDEE Calculator to apply an editable activity factor, or the Calorie Calculator to compare deficit and surplus scenarios.
When to Use It
Use this calculator when you need a reproducible adult estimate of resting energy, want to compare equations, or need to understand how a lean-mass formula differs from height-weight-age models. Use current measurements rather than a goal weight. Review the BMR Calculator assumptions before relying on this result for decisions.
When clinical accuracy matters, an appropriately conducted indirect-calorimetry assessment is more relevant than a prediction equation.
How the Calculation Works
For “How the Calculation Works,” the BMR Calculator organizes the relevant inputs, applies the documented method, and shows a result that can be compared across scenarios. The points below identify the specific considerations and assumptions users should review before relying on the estimate.
- The calculator validates age, height, weight, body-fat percentage, formula, and unit choices.
- U.S. measurements are converted to centimeters and kilograms.
- All three BMR equations run without intermediate display rounding.
- The selected formula becomes the headline daily estimate.
- The engine derives kilojoules, hourly energy, weekly energy, lean mass, and formula spread.
- The charts and table display all formula estimates with text alternatives.
Review the complete BMR formulas or follow the step-by-step BMR guide.
Common BMR Calculator Mistakes
- Treating BMR as maintenance calories or TDEE.
- Entering a goal weight instead of current body weight.
- Mixing pounds with kilograms or inches with centimeters.
- Using Katch-McArdle with a guessed body-fat percentage.
- Assuming the hourly and weekly figures are separate measurements.
- Selecting whichever formula produces the preferred answer.
- Treating the displayed result as clinical measurement precision.
Frequently Asked Questions
What is BMR?
Basal metabolic rate is the energy your body uses at rest to support essential functions. This calculator estimates that rate from published equations; it does not measure metabolism. Review the BMR Calculator assumptions before relying on this result for decisions.
Is BMR the same as TDEE?
No. BMR estimates resting energy. TDEE adds activity and other daily energy use. Use the TDEE Calculator when you need an activity-adjusted daily estimate. Use realistic inputs and review the BMR Calculator assumptions before relying on this result for decisions.
Which BMR formula should I use?
Mifflin-St Jeor is the default adult estimate. Revised Harris-Benedict is a useful comparison. Katch-McArdle uses estimated lean mass and therefore depends on the body-fat percentage you enter. Use realistic inputs and review the BMR Calculator assumptions before relying on this result for decisions.
Why do the BMR formulas give different results?
Each equation was developed from different data and predictors. The comparison chart shows the model spread for the same entries so the uncertainty stays visible. Use realistic inputs and review the BMR Calculator assumptions before relying on this result for decisions.
Is a BMR calculator accurate?
It is a population-based estimate. Individual error can be meaningful, and measured resting energy expenditure requires an appropriate indirect-calorimetry protocol. For a useful BMR Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
Can I use BMR as my calorie target?
BMR excludes ordinary movement and exercise, so it is not the same as maintenance calories. Use the Calorie Calculator for a transparent activity-adjusted estimate. Use realistic inputs and review the BMR Calculator assumptions before relying on this result for decisions.
Should I use current weight or goal weight for BMR?
Use current weight when estimating current resting energy. A goal weight does not describe your present body mass or present resting-energy estimate. For a useful BMR Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
Does exercise change the BMR result?
Exercise is not entered directly in these equations. BMR estimates resting energy. Activity belongs in a TDEE or maintenance-calorie calculation. For a useful BMR Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
Why does Katch-McArdle need body fat?
Katch-McArdle estimates lean body mass from weight and body-fat percentage, then uses lean mass to estimate BMR. Body-fat error therefore changes the result. For a useful BMR Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
What does formula spread mean?
Formula spread is the highest estimate minus the lowest for the same inputs. It shows model disagreement, not a confidence interval or guaranteed error range. Use realistic inputs and review the BMR Calculator assumptions before relying on this result for decisions.
One Useful Fact
The hourly and weekly figures contain no additional metabolic assumptions. They are simply the selected daily estimate divided by 24 or multiplied by seven.
Conclusion
A BMR calculator is most useful as a transparent resting-energy estimate. Compare equations, understand which inputs each formula uses, and continue to a TDEE calculation when the question involves total daily energy.