One-rep max (1RM) calculator
Estimate your one-rep max (1RM) and the loads to train at different intensities.
Epley formula. Estimate — do not attempt a true 1RM without supervision and warm-up.
How the calculation works
Your 1RM is the heaviest load you could lift once with good form. Testing it for real requires a long warm-up, solid technique and ideally a spotter — which is why it is almost always estimated from a submaximal set.
1RM = weight × (1 + reps ÷ 30) (Epley formula)
Step-by-step example
You lifted 176 lb for 5 reps:
- 5 ÷ 30 = 0.167
- 1 + 0.167 = 1.167
- 176 × 1.167 = 205 lb
Accuracy falls as reps rise
Up to 5 reps the estimate is good. Between 6 and 10 it still works for programming. Above 10 it becomes a rough approximation, because it starts depending heavily on individual muscular endurance rather than maximal strength — two people with the same true 1RM may manage 12 and 20 reps at the same load.
What the percentages are for
| % of 1RM | Typical reps | Main goal |
|---|---|---|
| 85% to 95% | 1 to 5 | maximal strength |
| 67% to 85% | 6 to 12 | hypertrophy |
| 50% to 67% | 13 or more | muscular endurance |
The ranges overlap deliberately: they are programming references, not physiological boundaries. Total volume and proximity to failure matter as much as the percentage.
Examples
- 80 kg for 5 reps: 1RM ≈ 80 × (1 + 5/30) = 93 kg.
- With a 100 kg 1RM, hypertrophy training (75%): 75 kg.
Frequently asked questions
How many reps to use?
The estimate is more accurate with up to ~10 reps.
Is it safe to test a true 1RM?
Only with good form, warm-up and ideally a spotter. For most people, the rep-based estimate is safer.
Why know your 1RM?
To program training by percentages (strength, hypertrophy, endurance) and track strength progress.
Are there formulas other than Epley?
Yes — Brzycki and Lombardi are the best known. They differ little up to 5 reps and more beyond 10, with Epley tending to estimate slightly higher on long sets. For tracking progress, what matters is consistently using the same one.
Does 1RM apply to every exercise?
It works best on stable compound lifts such as squat, bench press and deadlift. On isolation exercises, or lifts with heavy technical demands, the load-to-reps relationship is less predictable.
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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources