How this calculator works
Enter the weight you lifted and how many clean reps you completed, and this calculator estimates your one-rep max (1RM) using the Epley formula, with the Brzycki formula shown alongside for comparison. It also breaks down roughly what weight corresponds to each percentage of your 1RM, useful for programming training loads. Estimates are for training planning, not medical advice — max-effort testing carries injury risk and belongs under experienced supervision.
Rep-max formulas are estimates built from population data on submaximal sets, not a substitute for testing. They tend to agree closely in the 4-10 rep range and diverge more the higher the rep count goes, since a formula built around explosive low-rep strength does not describe fatigue the same way a 15-rep set does.
The formulas
Epley (1985): 1RM = weight × (1 + reps ÷ 30)Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)At exactly 1 rep, the lift itself is the one-rep max by definition, so both formulas return the weight lifted unchanged. The percent-of-1RM table estimates typical reps at each intensity by solving the Brzycki formula for reps.
Worked example: 200 lb for 5 reps
- Epley: 200 × (1 + 5 ÷ 30) = 200 × 1.1667 ≈ 233.3 lb estimated 1RM.
- Brzycki: 200 × 36 ÷ (37 − 5) = 7,200 ÷ 32 = 225 lb estimated 1RM.
- At 80% of the Epley estimate: 233.3 × 0.80 ≈ 186.7 lb, a load typically good for around 8 reps.
- The two formulas agree exactly at 10 reps, where both multipliers equal 1.3333.
Frequently asked questions
Why do Epley and Brzycki give different numbers?
They were fit to different data sets. They agree closely in the middle rep ranges and diverge more at the extremes — Brzycki tends to run lower at higher rep counts.
How accurate is this above 10 reps?
Less accurate. Rep-max formulas are built on strength-endurance relationships that hold reasonably well up to about 10 reps; beyond that, fatigue and technique breakdown make the estimate increasingly unreliable.
Should I actually test my true 1RM instead?
A supervised, properly warmed-up 1RM test with a spotter is more accurate, but carries injury risk if attempted without guidance. This calculator is meant to estimate your max without loading a bar to failure.
Does the unit (lb vs kg) change the formula?
No. Both formulas are unit-agnostic multipliers applied to whatever weight you enter, so the result is simply in the same unit as your input.
How do I use the percent-of-1RM table to choose a training weight?
Find the percentage that matches your training goal, then multiply your estimated 1RM by that percentage to get a target weight — the table does this multiplication across a range of common percentages automatically. In the worked example, 80% of the 233.3 lb estimated 1RM is about 186.7 lb, a load the table associates with roughly 8 reps.