Your one rep max (1RM) is the heaviest weight you could lift for a single perfect repetition. Testing it directly is risky and tiring — this calculator estimates it safely from a working set, using two proven formulas, and gives you a full percentage table for planning your training.
One Rep Max Calculator
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Estimate only — not medical advice.
How the One Rep Max Calculator Works
The calculator runs your set through two well-known formulas and averages them:
- Epley formula: 1RM = weight × (1 + reps ÷ 30)
- Brzycki formula: 1RM = weight × 36 ÷ (37 − reps)
Estimates are most accurate with sets of 2–10 reps. Above 12 reps the formulas drift, because endurance starts to matter more than strength.
Worked Example
You squat 100 kg for 5 reps. Epley: 100 × (1 + 5/30) = 116.7 kg. Brzycki: 100 × 36/32 = 112.5 kg. Average estimated 1RM ≈ 115 kg. Your 80% training weight would be about 92 kg.
How to Use the Percentage Table
- 90–100%: Strength peaks and testing — 1–3 reps.
- 75–85%: The main muscle-and-strength zone — 4–8 reps.
- 60–70%: Volume work, technique and speed — 8–15 reps.
Frequently Asked Questions
How accurate is a calculated 1RM?
For sets of 2–10 reps, estimates are usually within about 5% of a true tested max. Treat the number as a planning tool, not a promise.
Is it safe to test my real 1RM?
A true max attempt carries injury risk and needs a spotter, good form and a proper warm-up. Most lifters get everything they need from calculated estimates.
Which formula is better, Epley or Brzycki?
Epley tends to read slightly higher, Brzycki slightly lower. The average of the two is a sensible middle estimate.
Does the formula work for every exercise?
It works best for barbell compound lifts (squat, bench press, deadlift, overhead press). Machine and isolation exercises are less predictable.