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One-rep max calculator
Estimate your one-rep max from any hard set — including the reps you had left in the tank. Every other calculator silently assumes your set went to failure. If you stopped at 2 reps in reserve, they underestimate you. This one asks.
RIR chart — percentage of 1RM
What a set at a given rep count and reps in reserve says about your max. Read across: 8 reps with 2 in reserve means the load was about 77% of your one-rep max.
| Reps | RIR 0 — failure | RIR 1 | RIR 2 | RIR 3 | RIR 4 |
|---|---|---|---|---|---|
| 1 | 100% | 97% | 94% | 91% | 88% |
| 2 | 97% | 94% | 91% | 88% | 86% |
| 3 | 94% | 91% | 88% | 86% | 83% |
| 4 | 91% | 88% | 86% | 83% | 81% |
| 5 | 88% | 86% | 83% | 81% | 79% |
| 6 | 86% | 83% | 81% | 79% | 77% |
| 7 | 83% | 81% | 79% | 77% | 75% |
| 8 | 81% | 79% | 77% | 75% | 73% |
| 9 | 79% | 77% | 75% | 73% | 71% |
| 10 | 77% | 75% | 73% | 71% | 70% |
Quiet values are efforts past 10 reps to failure, where every 1RM formula loses accuracy — treat them as rough.
Why RIR changes the math
1RM formulas convert a repetition effort into a max — but only if they know the true effort. A set of 8 stopped with 2 reps in reserve is a 10-rep effort, and feeding it to a standard calculator as “8 reps” understates what you are capable of by roughly 7%.
Since most hypertrophy training deliberately stops short of failure, most sets you would actually plug in here were not maximal. Counting the reps you left in reserve is what makes the estimate honest. New to the idea? What reps in reserve means.
The formula, exactly
1RM = weight × (1 + (reps + RIR − 1) ÷ 30)
100 × (1 + (8 + 2 − 1) ÷ 30)
= 100 × 1.30
= 130 kgThis is Epley with two corrections: reps in reserve count toward the effort, and the −1 makes a true single return exactly its own weight, where standard Epley returns 103.3%. Brzycki (weight × 36 ÷ (37 − reps to failure)) is shown alongside every result for comparison.
Where estimates break down. All 1RM formulas degrade past about 10 reps to failure, and none of them accounts for your leverages, the lift, or the day. Treat any estimate as a planning number, not a promise — the best data comes from sets of 3–8 taken close to failure.
Work backwards: plan a set from your max
The direction you actually need when programming — what load hits a target rep count at a target reps in reserve.
Common questions
Can I use this as a 5-rep max or 3-rep max calculator?
Yes. Every result includes your estimated 2RM, 3RM, 5RM, 8RM and 10RM, derived from the same formula run in reverse.
What if my set actually went to failure?
Set reps in reserve to 0. With nothing left in the tank this calculator behaves like a conventional one — that is the special case every other calculator assumes.
Why is my number lower than on other calculators?
Two reasons. Standard Epley overestimates by design, returning about 103% of the bar weight for a true single, which this page corrects. And if you entered a reps-in-reserve above 0, other calculators are scoring an easier set as though it were maximal.
Is RIR the same as RPE?
They are inverses on the same scale: RPE is roughly 10 minus RIR, so a set at RIR 2 is RPE 8. There is more in RPE vs RIR.
How accurate is an estimated one-rep max?
Close enough to program from, not close enough to attempt blind. Estimates are most reliable from sets of three to eight taken near failure, and they degrade past about ten reps to failure. None of these formulas knows your leverages, the lift, or how the day is going.
Stop recalculating
Log load, reps and RIR on every set and RIRLift keeps your estimated 1RM current for every lift — from every working set, not just heavy singles.
It makes it super easy to track my exercises and progress. My favorite part is being able to see the exact muscles each exercise trains