1RM calculator
Estimate your one rep max from a set you've already done — five classic formulas side by side, so you can see how much they actually disagree.
| Formula | 1RM |
|---|
More accurate: add how hard the set feltThe RPE method accounts for the reps you had left — that's what these formulas miss.
Use the RPE calculator →Why the formulas disagree
Every formula here takes the same two inputs — weight and reps — and each one bends the curve differently. At 3 reps they'll land within a couple of kilos of each other. At 10 reps the spread can be 10% or more, because how many reps you can do at a given percentage varies enormously between people. A lifter with high rep endurance and one with none can share the exact same 1RM and produce wildly different sets of 10.
What each one does
Epley — the most common; generous at higher reps.
Brzycki — more conservative as reps climb.
Lombardi — power curve, sits between the two.
O'Conner — simple linear model, conservative.
Lander — close to Brzycki in most of the range.
The more accurate way: RPE
The blind spot in all five is that they assume your set went to failure. A set of 5 with 2 reps left is a completely different data point from a set of 5 that nearly killed you — but these formulas treat them identically.
The RPE method fixes exactly that: you rate how close the set was, and the estimate uses that rating. Same set, honest number. That's what the RPE calculator does, and it's why RPE-based programming has largely replaced fixed percentages in powerlifting.
How to use your estimated max
Once you have a number, everything else follows: training percentages, the RPE chart for target weights, what to load on the bar, and your DOTS score if you're heading to a meet.
One caution: re-estimate regularly. An e1RM from six weeks ago is a historical fact, not your current strength.
Questions
How accurate is a 1RM calculator?
Good under about 6 reps and when the set was genuinely close to failure. Above 8–10 reps treat the number as a ballpark, not a target.
Which formula should I use?
For low reps it barely matters. If you want one number, the average shown above is a sensible compromise. If you can rate your RPE, that method beats all of them.
Can I calculate my max without ever testing one?
Yes — that's the entire point. Most lifters never test a true max outside a meet and program from estimates instead.
Every number, in your pocket
The app does this offline between sets: estimated max, next set's weight, the plates to load and your warm-up.
Download on Google Play Launching on Google Play — final testingFree download · Pro is a single one-time unlock · No subscription