What this calculator does
A one-rep max, or 1RM, is the heaviest weight a lifter could manage for a single complete rep of a given exercise. Testing it directly is fatiguing and carries injury risk, so most lifters estimate it instead from a lighter set taken close to failure, using one of several formulas built for that purpose.
This 1RM calculator applies four widely used formulas, Epley, Brzycki, Lombardi and Wathan, to the same weight and rep count, and works for any lift rather than being tied to one exercise, since the underlying formulas only need a weight and a rep count to work from.
The formula
Each formula extrapolates from a submaximal set to an estimated single-rep maximum differently: Epley assumes a roughly linear relationship between reps and load, Brzycki fits a formula that approaches its limit as reps rise, Lombardi uses a power relationship, and Wathan uses a fitted exponential curve. None are exact; they typically agree within a few kilograms of each other at moderate rep counts and diverge more at high rep counts.
| Term | Meaning |
|---|---|
| 1RM | The estimated maximum weight liftable for one complete rep. |
| Weight lifted | The load used for the set the estimate is based on. |
| Reps performed | The number of reps completed at that weight, ideally close to failure. |
The inputs explained
| Field | What to enter |
|---|---|
| Weight lifted (kg) | The weight used for the set, in whichever unit you normally track. |
| Reps performed to failure | The number of reps completed with that weight, taken close to failure for the most reliable estimate. |
| Formula to highlight | Which formula to highlight as the main result, or an average of all four. |
When to use it
Estimating a 1RM without testing it directly
Working from a recent set of, say, 5 or 8 reps avoids the fatigue and injury risk of attempting a true single-rep maximum, while still giving a workable estimate to plan training around.
Setting percentage-based training loads
Many strength programmes prescribe work at a percentage of 1RM, such as 80% for a strength block; the percentage table below converts the estimate straight into those working weights.
Comparing formulas when reps are high
The four formulas agree closely at low to moderate reps but spread apart as rep count rises, particularly Brzycki, which becomes unreliable and eventually undefined above around 36 reps; checking more than one formula flags when an estimate is drifting.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the estimated 1RM changes with reps performed, at a fixed weight
A fixed 80 kg, across a range of rep counts, using the average of all four formulas.
Questions
What is a 1RM calculator?
A tool that estimates the heaviest weight a lifter could manage for one rep of an exercise, based on a lighter weight lifted for more than one rep, using a formula fitted to that relationship.
Which 1RM formula is most accurate?
None is exact for everyone; accuracy varies by individual, exercise and rep range. Epley and Brzycki are the two most commonly cited, and averaging several formulas, as this calculator can do, smooths out some of the disagreement between them.
How many reps should I use to estimate my 1RM?
Somewhere in the 3 to 10 rep range, taken close to failure, generally gives the most reliable estimate. Very high rep sets push every formula further from its comfort zone and produce less trustworthy results.
Does this work for exercises other than bench press?
Yes. The four formulas used here only need a weight and a rep count, so they apply equally to squat, deadlift, overhead press or any other single-rep-max lift, not just bench press.
For a bench-press-specific single-formula version of the same idea, see the bench press 1RM calculator.