1RM calculator
This 1RM calculator estimates your one-rep max from a set you've already done — no maxing out, no spotter, no risk. Enter the weight and how many reps you got, and you'll get an estimate from four published formulas plus the training percentages that come off it.
Percentage of 1RM table
What each percentage of your max weighs, and roughly how many reps it should allow.
| % of 1RM | Reps | Weight |
|---|---|---|
| 100% | 1 | — |
| 95% | 2 | — |
| 90% | 3 | — |
| 85% | 5 | — |
| 80% | 8 | — |
| 75% | 10 | — |
| 70% | 13 | — |
| 65% | 16 | — |
| 60% | 20 | — |
How the formulas differ
All four multiply your set by a factor that grows with reps; they just disagree about how fast.
- Epley —
w × (1 + reps ÷ 30). The default in most apps, including Tanko. - Brzycki —
w × 36 ÷ (37 − reps). Slightly lower at high reps. - Lombardi —
w × reps^0.10. The most conservative of the four. - O'Conner —
w × (1 + 0.025 × reps). The simplest to do in your head.
They agree closely at 1–5 reps and drift apart above 10, which is the real rule: estimate from heavy sets. A set of 12 tells you much less about your max than a set of 3.
What to do with the number
An estimated 1RM (e1RM) is most useful as a trend, not a trophy. Programs are written in percentages — 5×5 at 80%, singles at 90% — and the table above turns your estimate into those loads. Track the estimate across months and it becomes the cleanest single measure of whether a lift is actually progressing, because it moves whether you added weight or added reps.
Tanko computes an e1RM from every set you log and charts it per exercise, so the trend is a side effect of training instead of a spreadsheet chore. See also our guide to estimating your one-rep max.
Frequently asked questions
How accurate is a 1RM calculator?
Within a few percent when the set is heavy — 1 to 5 reps — and progressively looser above that. Rep-max formulas assume an average strength-endurance profile; if you're unusually good at high reps, they'll overestimate you.
Which 1RM formula should I use?
Pick one and stay with it. Consistency matters far more than the choice, because the value of an e1RM is in comparing it to your own previous e1RM. Epley is the most common default.
Should I actually test my 1RM?
Rarely, and only if you compete. A true max costs a heavy session and some recovery. For everyone else the estimate is enough to program with.
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