How to calculate your 1RM without maxing out
By Andreas Lee-Norman · Updated · 2 min read
Take a set you did with good form for 2–10 reps and multiply the weight by (1 + reps ÷ 30). That's the Epley formula, and it estimates the heaviest single rep you could lift. 100 kg for 5 reps gives an estimated 1RM of about 117 kg — no max attempt needed.
What is a one-rep max?
Your one-rep max (1RM) is the most weight you can lift for one full, controlled repetition of an exercise. It's the standard yardstick for strength, and most training programs describe loads as a percentage of it — "5 sets of 5 at 80%".
Testing a true 1RM is tiring, needs a spotter for lifts like the bench press, and carries more risk than normal training. The good news: you can estimate it accurately from the sets you already do.
The two formulas worth knowing
| Formula | Calculation | 100 kg × 5 reps |
|---|---|---|
| Epley | weight × (1 + reps ÷ 30) | 116.7 kg |
| Brzycki | weight × 36 ÷ (37 − reps) | 112.5 kg |
Both formulas agree closely up to about 10 reps. Above 10–12 reps they drift apart and become less reliable, because endurance starts to matter as much as strength. For the best estimate, use a heavy set of 3–6 reps taken close to — but not at — failure.
Don't want to do the maths? Use the free 1RM calculator: it shows both formulas, their average, and a table of training weights.
How to estimate your 1RM, step by step
- Warm up with a few lighter sets of the exercise.
- Do one hard set of 3–6 reps with a weight you can move with good form. Stop when the next rep would be a grind.
- Plug in weight and reps. Epley: weight × (1 + reps ÷ 30).
- Round down to the nearest plate increment (2.5 kg or 5 lb) when you use it to plan training.
Using your 1RM to choose training weights
Once you know your estimated 1RM, percentages make weight selection simple. A common guide:
- 85–95% — heavy strength work, 1–5 reps
- 70–85% — the classic muscle-building range, 6–12 reps
- 50–70% — technique, speed and higher-rep work
These ranges vary between people and exercises — treat them as a starting point and adjust by how the sets feel.
Track your estimated 1RM over time
A single estimate is a snapshot. The real value comes from watching it climb. Gym Companion calculates your estimated 1RM with the Epley formula from every set you log and draws it as a chart over 1 month, 3 months or all time — so you see progress even in weeks when you never test a max.
Frequently asked questions
How accurate is a 1RM estimate?
For sets of 10 reps or fewer, the Epley and Brzycki formulas usually land close to a tested max. Accuracy drops with higher reps and varies with training experience, so treat the result as a well-informed estimate rather than an exact number.
Should I test my real 1RM?
You don't have to. Estimating from regular working sets tracks strength every session without the fatigue and risk of a max attempt. If you compete or want to test, do it with a spotter and a proper warm-up.
Does the formula work for every exercise?
It works best for compound lifts like the squat, bench press, deadlift and overhead press. For small isolation exercises such as curls or lateral raises, 1RM estimates are less meaningful.