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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 (7 or harder) for a more accurate number off the RTS chart that accounts for how many reps you had left. A set rated below 7 is scored by Epley, the same as leaving RPE blank. Works in pounds or kilograms.
| % of 1RM | Weight |
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RPE 10 = no reps left, 9 = about one left, 8 = about two. Add it for a sharper estimate at RPE 7 or harder; leave it blank, or rate the set below 7, and the Epley formula is used, because easy-set ratings are the least reliable. Sets longer than 10 reps are not estimated, because neither method predicts a max from them.
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, and it reads high once the reps climb. - 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. A rating below RPE 7 is not used, and the set is scored by Epley instead: lifters judge how many reps they have left least accurately when they are far from failure, whatever their experience (Halperin et al., 2022, a meta-analysis of 12 studies), and an easy rating inflates the estimate the most. Ægir Iron applies the same rule to every estimate it shows. Past 10 reps there is no estimate at all: the chart has no row that long and Epley reads systematically high there, so both this calculator and the app say so instead of printing a number.
Sources: the reps by RPE chart is the Reactive Training Systems (RTS) chart popularized by Mike Tuchscherer; the reps-in-reserve-based RPE scale the chart uses is described in Zourdos et al. (2016) and Helms et al. (2016). Neither paper validates the chart's percentages, which come from RTS. 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), for sets up to 10 reps; adding an RPE of 7 or harder 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? RPE is Rate of Perceived Exertion, rated on a 1 to 10 scale; the RPE chart covers 6 to 10. RPE 10 means no reps left in the tank, RPE 9 means about one rep left, RPE 8 about two, and so on. It captures proximity to failure, which is what makes an RPE-aware 1RM estimate more accurate.
Pounds or kilograms? Both. The estimate is a ratio, so it comes back in whatever unit you enter.