Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
BMR
1,706
calories/day at complete rest
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter units.
- 2Enter sex.
- 3Enter age (years).
- 4Enter weight.
- 5Enter height.
- 6Read your bmr on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
Mifflin-St Jeor equation, the most accurate BMR formula for most adults.
Worked example
Using the values the calculator loads with:
Inputs
- Units: Imperial (lb, in)
- Sex: Male
- Age: 30 years
- Weight: 170
- Height: 68
Results
- BMR: 1,706
What each field means
Inputs
- Units
- Pick the option that matches your situation — the maths changes per option. Choices: Metric (kg, cm), Imperial (lb, in).
- Sex
- Pick the option that matches your situation — the maths changes per option. Choices: Male, Female.
- Age (years)
- The age used in the calculation, measured in years. Starts at 30 years so you have a working example on load. Accepted range: 1–120 years.
- Weight
- The weight used in the calculation. Starts at 170 so you have a working example on load.
- Height
- The height used in the calculation. Starts at 68 so you have a working example on load.
Results
- BMR
- calories/day at complete rest
FAQ
How does the bmr calculator work?
Mifflin-St Jeor equation, the most accurate BMR formula for most adults. The underlying maths is: Mifflin-St Jeor: 10·kg + 6.25·cm − 5·age + s (s=+5 male, −161 female).
What do I need to enter?
5 values: units, sex, age, weight, and height. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the bmr result mean?
calories/day at complete rest It is returned as a whole number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
Who is this tool for?
It's built for anyone tracking a health or training target and wanting the standard formula applied correctly, without a signup or an app.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). BMR Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/bmr
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/bmr" target="_blank" rel="noopener">BMR Calculator — RevenueLab</a> (2026).</p>
Source: [BMR Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/bmr) (2026).