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 →How do you calculate your 1RM?
Take a set you performed and enter the weight and the number of reps. The calculator applies a rep-to-percentage formula to estimate the load you could lift once. For example, 100 kg for 5 reps gives an estimated one rep max of roughly 113 to 117 kg depending on the formula used.
How accurate is a 1RM calculator?
Estimates are reliable when the set was close to failure and under about six reps. Above eight to ten reps the formulas drift apart and tend to overestimate, because rep endurance varies far more between lifters than maximal strength does.
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