Estimate your one-rep max with 7 formulas, see a percentage chart, use RPE, find training zones and build a warm-up.
1RM (one-repetition maximum) is the heaviest load you can lift once with correct technique. Because testing is risky and tiring, people use a submaximal set to failure and empirical formulas: Epley (load x (1 + reps/30)), Brzycki (load x 36 / (37 - reps)), Lander, Lombardi, Mayhew, O'Conner and Wathan. At 100 kg x 5, Epley gives 116.7 kg and Brzycki 112.5 kg; the tool shows all seven, the average and the range. Accuracy is decent up to about 10 reps and drops after that, and Brzycki is undefined from 37 reps. With a 1RM in hand you get a percentage chart (50% to 100%) rounded to the smallest plate you own, typical reps for each band, the load for a target rep count, RPE converted to load through the reps-in-reserve chart, training zones (strength from 85%, hypertrophy 67 to 85%, endurance up to 67%, NSCA teaching labels) and a warm-up ramp up to your working load. Everything is an estimate, not a prescription: the day's form, technique and the lift all change the result.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
<iframe
src="https://jkit.tools/embed/en-US/one-rep-max-calculator"
width="100%"
height="600"
style="border:0"
loading="lazy"
title="One Rep Max Calculator"
></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
It is the heaviest load you can lift for a single full repetition with correct technique in a given exercise. It is a reference for dosing training in percentages, not a goal and not something you are obliged to test.
| Formula | 1RM (kg) |
|---|---|
| Epley | 116.7 |
| Brzycki | 112.5 |
| Lander | 113.7 |
| Lombardi | 117.5 |
| Mayhew | 119 |
| O'Conner | 112.5 |
| Wathan | 116.6 |
Each formula is a regression fitted to specific groups and lifts, so the values differ. Averaging the seven reduces the bias of any one, but does not remove the error.
The fraction of 1RM each formula assigns to each rep count. They agree closely at low reps and drift apart as reps grow.
| Reps | Epley | Brzycki | Lander | Lombardi | Mayhew | O'Conner | Wathan |
|---|---|---|---|---|---|---|---|
| 1 | 100% | 100% | 100% | 100% | 100% | 100% | 100% |
| 2 | 93.8% | 97.2% | 96% | 93.3% | 89.7% | 95.2% | 95.1% |
| 3 | 90.9% | 94.4% | 93.3% | 89.6% | 87.7% | 93% | 91.8% |
| 4 | 88.2% | 91.7% | 90.6% | 87.1% | 85.8% | 90.9% | 88.7% |
| 5 | 85.7% | 88.9% | 87.9% | 85.1% | 84% | 88.9% | 85.8% |
| 6 | 83.3% | 86.1% | 85.3% | 83.6% | 82.3% | 87% | 83.1% |
| 8 | 78.9% | 80.6% | 79.9% | 81.2% | 79.2% | 83.3% | 78.3% |
| 10 | 75% | 75% | 74.6% | 79.4% | 76.4% | 80% | 74.2% |
| 12 | 71.4% | 69.4% | 69.2% | 78% | 73.9% | 76.9% | 70.7% |
| 15 | 66.7% | 61.1% | 61.2% | 76.3% | 70.6% | 72.7% | 66.3% |
This is a mathematical estimate, not a real test or a training prescription. Only attempt a true 1RM with good technique, a warm-up, safety pins or a spotter, ideally under professional supervision. If you have an injury or a health condition, talk to a professional first.