1RM calculator
Same formula as the Overload app
This 1RM calculator estimates your one-rep max from a set you have already done: enter the weight and the number of reps, and get the load you could lift once. It uses the same banded formula as the Overload app, which averages Epley and Brzycki at low reps and switches to Wathen and Mayhew as reps rise, so the estimate stays stable from 1 to 30 reps. The percentage table below gives you working loads for any programme written in % of 1RM.
Estimated 1RM
114.6kg
High confidence
Percentage table
| % of 1RM | Load (kg) | Reps |
|---|---|---|
| 100 % | 114.6 | 1 |
| 95 % | 108.9 | 1 |
| 90 % | 103.1 | 3 |
| 85 % | 97.4 | 5 |
| 80 % | 91.7 | 7 |
| 75 % | 85.9 | 9 |
| 70 % | 80.2 | 12 |
| 65 % | 74.5 | 16 |
| 60 % | 68.8 | 20 |
| 55 % | 63.0 | 24 |
| 50 % | 57.3 | 30 |
By formula
How it works
No single equation is accurate across all rep ranges. Linear formulas such as Brzycki diverge above 10 reps, while exponential ones such as Wathen and Mayhew plateau. The calculator therefore picks the formula by rep count: a single is its own max, 2 to 6 reps average Epley and Brzycki, 7 to 10 reps average Epley and Wathen, 11 to 15 reps use Wathen alone, and 16 to 30 reps blend Wathen into Mayhew.
The confidence label follows the same bands. Every formula assumes the set was close to failure, so a comfortable set underestimates your max. Sets above 30 reps are excluded because they measure endurance, not maximal strength (Reynolds 2006, Mayhew 2008).
The percentage table inverts Epley to give the reps you can expect at each percentage. Use it to convert a programme written in % of 1RM into kilograms on the bar.
Frequently asked questions
Which 1RM formula is the most accurate?
For sets of 2 to 6 reps, Epley and Brzycki agree within a few percent and both are accurate. Above 10 reps, Wathen and Mayhew are more reliable because they do not grow without bound. That is why this calculator averages formulas by rep range instead of relying on one.
Should I test my real 1RM?
Most lifters do not need to. An estimate from a hard set of 3 to 5 reps is close enough to program from and carries far less injury risk. Test a true max only if you compete, and after a proper taper.
Why does my estimate change between sets?
The formulas assume the set was taken close to failure. A warm-up set or an easy back-off set will read low. Use your heaviest set of the session, which is what the Overload app does when it tracks your e1RM over time.
Related tools
- Plate calculatorWork out exactly which plates to load per side for any barbell weight, free, with the achieved load and shortfall shown instantly.
- Warm-up sets calculatorBuild a free warm-up ladder of sets leading into your working weight, so every jump between the bar and your top set is planned.
- RPE calculatorConvert any set to a percentage of your 1RM or a target load from RPE, free, with a full table of reps against RPE 6 to 10.
- Strength standardsFind your strength level on the squat, bench, deadlift, press or row, free, with the weight needed to reach the next level shown.
Track your 1RM over time in Overload
Log your sets and Overload estimates your 1RM per exercise after every session, with the same formula, and charts your progress. Free on iOS and Android.