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One-Rep Max Calculator
Estimate your one-rep max from a set you actually lifted. Enter the weight and reps for an Epley estimate, or add your RPE for a more accurate number off the RTS chart that accounts for how many reps you had left. Works in pounds or kilograms.
| % of 1RM | Weight |
|---|
RPE 10 = no reps left, 9 = about one left, 8 = about two. Add it for a sharper estimate; leave it blank and the Epley formula is used.
How the estimate works
There are two ways to turn a set into a one-rep max, and this calculator uses the better one whenever it can:
- Reps only (Epley):
1RM = weight x (1 + reps / 30). Simple and standard, but it treats every set of five the same, whether it was easy or a grind. - Reps + RPE (RTS chart): your weight divided by the percentage of 1RM implied by the reps-by-RPE chart. Because RPE captures how close to failure you were, five reps at RPE 7 and five at RPE 10 correctly return different maxes.
This is the same RTS / Tuchscherer chart Ægir Iron uses to read your logged sets and to translate an RPE prescription into a working weight, so the number is consistent whether you are estimating a max or following a program. RPE inputs outside the chart's range (reps 1 to 10, RPE 6 to 10) fall back to Epley rather than guessing.
Sources: the reps by RPE chart is the Reactive Training Systems (RTS) chart popularized by Mike Tuchscherer; the RPE-to-percentage-of-1RM relationship is supported by Zourdos et al. (2016) and Helms et al. (2016). The reps-only fallback uses the Epley formula (1985).
Using the percentage table
Once you have an estimated 1RM, the table gives you the common training percentages, from 100% down to 60%. Powerlifting and weightlifting programs are written in these percentages, so this is the bridge from "what can I do for one" to "what should I load today."
Common questions
How do you calculate your one-rep max? From a set you did: enter weight and reps. Reps alone uses Epley, 1RM = weight x (1 + reps / 30); adding RPE reads your percentage off the RTS chart, which is more accurate.
What's the most accurate way to estimate a 1RM? Reps and RPE together, because proximity to failure matters: five reps at RPE 7 and five at RPE 10 imply different maxes.
What is RPE? Rate of Perceived Exertion, 6 to 10. RPE 10 is no reps left, 9 is about one left, 8 about two.
Pounds or kilograms? Both. The estimate is a ratio, so it comes back in whatever unit you enter.