1RM calculator (one-rep max)
Estimate your one-rep max from a submaximal set and see the suggested load for each rep range.
Your estimated 1RM 1RM (one-rep max) 1RM is the heaviest load you can lift for a single repetition with good technique in a given exercise.
91.7 kg
Epley 93.3 kg · Brzycki 90 kg
| % of 1RM 1RM (one-rep max) 1RM is the heaviest load you can lift for a single repetition with good technique in a given exercise. See in glossary → | Load | Approx. reps |
|---|---|---|
| 100% | 91.7 kg | ~1 |
| 95% | 87.1 kg | ~2 |
| 90% | 82.5 kg | ~4 |
| 85% | 77.9 kg | ~6 |
| 80% | 73.3 kg | ~8 |
| 75% | 68.8 kg | ~10 |
| 70% | 64.2 kg | ~12 |
| 65% | 59.6 kg | ~15 |
| 60% | 55 kg | ~18 |
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Terms used in this calculator
These concepts show up in the math and help you read the result with more context.
- 1RM (one-rep max)
- 1RM is the heaviest load you can lift for a single repetition with good technique in a given exercise.
- RPE (rating of perceived exertion)
- RPE is an effort scale where RPE 10 equals failure (0 repetitions in reserve).
- RIR (reps in reserve)
- RIR is the number of repetitions you could still perform when you end a set.
What 1RM is and why you estimate it
Your 1RM is the heaviest load you can lift once with good technique on a given exercise. It works as a reference for programming intensity: many plans describe load as a percentage of your 1RM.
Testing a true 1RM means going to maximal loads and carries more risk. Estimating it from a submaximal set — five reps with something left in the tank, for example — is safer and more practical day to day.
How the math works
The calculator uses two classic formulas, Epley and Brzycki, and shows the average between them. They are most accurate in the 1 to 10 rep range; beyond that, the estimate loses precision.
Use the result as a starting point and adjust it with your perceived effort (RPE/RIR) and how the set actually moved — not as a fixed, definitive number.
Sources and references
- Source: Reynolds MJ, Gordon PM, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res, 2006. — Journal of Strength and Conditioning Research (PubMed)
Reviewed by the SelfShapeAI research team.
Frequently asked questions
How do I calculate my 1RM without testing a maximal load?
Enter the weight you used and how many reps you completed with good technique on a submaximal set. The calculator estimates your 1RM with the Epley and Brzycki formulas, so you avoid the risk of a true max attempt.
Which rep range is most reliable for estimating 1RM?
Between 1 and 10 reps. The closer to failure and within that range, the more accurate the estimate tends to be. Above 10 to 12 reps, the error grows.
Can I use an estimated 1RM to build my training?
Yes, as a reference. Use the percentages to set target loads, but adjust for how the lift actually moves and for the day's perceived effort — strength varies with sleep, food and fatigue.
Keep reading
Take the math into your training
SelfShapeAI builds the plan, logs your loads and adjusts volume with context — so you don't have to run the numbers by hand.
