The one-rep max, or 1RM (one-rep max), is the heaviest weight you can lift in a given exercise for one correct repetition. It is a key reference point in strength training — your working weights are calculated from it. Instead of risking injury during an attempt with a maximum load, you can safely estimate it from a formula.
Why know your 1RM?
Many training plans give intensity as a percentage of 1RM, for example 3 sets of 5 reps at 80 percent of 1RM. To use them, you need to know your maximum. Estimating 1RM from a formula lets you avoid a dangerous attempt at lifting a record weight, which risks injury without a spotter.
The Epley formula
The most popular is the Epley formula: 1RM = weight × (1 + number of reps / 30). You substitute the weight you lifted and the number of correct reps you performed. The formula is most accurate in the range up to about 10 reps — beyond that the estimates become less reliable.
Worked example
Suppose in the bench press you lifted 80 kg for 5 reps:
- We calculate the factor: 1 + 5 / 30 = 1 + 0.167 = 1.167.
- We multiply by the weight: 80 × 1.167 ≈ 93.3 kg.
- Your estimated 1RM is about 93 kg.
For comparison: if you had lifted 80 kg for only 3 reps, the result would be 80 × (1 + 3/30) = 88 kg — fewer reps translate into a lower estimated maximum at the same weight.
How to calculate working weights?
Knowing your 1RM, you can easily select loads for your training goal:
- Maximum strength: 85–100 percent of 1RM, 1–5 reps.
- Hypertrophy (mass): 67–85 percent of 1RM, 6–12 reps.
- Muscular endurance: below 67 percent of 1RM, 12 or more reps.
With an estimated 1RM of 93 kg, the weight for hypertrophy (75 percent) will be about 70 kg.
Safety rules
- Always warm up before a test set.
- For the estimate, use a weight you can lift with good technique for about 5–8 reps.
- Do not attempt a real maximum without experience and a spotter.
- If you feel pain or lose technique, stop the set immediately.
Limitations of the formula
Every formula is an approximation — the actual maximum depends on technique, the type of exercise and individual predispositions. Treat the result as a starting point for planning, not a rigid record value.
This guide is for information only and does not replace consultation with a coach or doctor. If you have illnesses or injuries, discuss your training plan with a specialist.
Estimate your 1RM with the Epley formula: 1RM calculator →