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
Estimated 1RM (avg)
212.0
Epley formula
215.8
Brzycki formula
208.1
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter weight lifted (lb/kg).
- 2Enter reps performed.
- 3Read your estimated 1rm (avg) on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
Uses the Epley and Brzycki formulas to estimate 1RM from a recent lift.
Worked example
Using the values the calculator loads with:
Inputs
- Weight lifted: 185 lb/kg
- Reps performed: 5
Results
- Estimated 1RM (avg): 212
- Epley formula: 215.8
- Brzycki formula: 208.1
What each field means
Inputs
- Weight lifted (lb/kg)
- The weight lifted used in the calculation, measured in lb/kg. Starts at 185 lb/kg so you have a working example on load.
- Reps performed
- The reps performed used in the calculation. Starts at 5 so you have a working example on load. Accepted range: 1–30.
Results
- Estimated 1RM (avg)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Epley formula
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Brzycki formula
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the 1rm calculator work?
Uses the Epley and Brzycki formulas to estimate 1RM from a recent lift.
What do I need to enter?
2 values: weight lifted, and reps performed. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the estimated 1rm (avg) result mean?
It is returned as a decimal 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). One Rep Max Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/one-rep-max
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/one-rep-max" target="_blank" rel="noopener">One Rep Max Calculator — RevenueLab</a> (2026).</p>
Source: [One Rep Max Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/one-rep-max) (2026).