Your one rep max (1RM) is the heaviest weight you could lift once with good form. Knowing it is genuinely useful — most sensible strength programmes set every working weight as a percentage of it. The problem is finding it by actually attempting a maximum lift.
A true max attempt is tiring, disrupts a week of training, and carries the highest injury risk of anything you do in the gym — especially without a spotter. Fortunately, you can estimate your 1RM accurately from an ordinary working set, and never test it directly at all.
The Two Estimation Formulas
Coaches use two classic formulas. The Epley formula: 1RM = weight × (1 + reps ÷ 30). The Brzycki formula: 1RM = weight × 36 ÷ (37 − reps). Each has a slight bias — Epley reads a touch high, Brzycki a touch low — so averaging them gives a sensible middle estimate.
Say you bench press 60 kg for 8 reps. Epley: 60 × (1 + 8/30) = 60 × 1.267 = 76.0 kg. Brzycki: 60 × 36 ÷ 29 = 74.5 kg. Average: an estimated 1RM of about 75 kg. Training at 80% would mean working sets around 60 kg — exactly the weight you started with, which is a good sanity check. Our One Rep Max Calculator runs both formulas and the average for you.
Getting a Reliable Estimate
- Use a set of 3–8 reps taken close to your limit, with clean technique. Estimates are at their best in this range.
- Avoid sets above 10–12 reps. Beyond that, endurance and discomfort distort the result and the formulas drift.
- Use your final hard set, not a warm-up, and be honest about whether the last rep was truly difficult.
- Compound lifts work best — squat, bench press, deadlift, overhead press. Machine and isolation exercises are less predictable.
One more trap: estimating from tired muscles. Always use a set performed fresh — after your warm-up sets, not at the end of a long session — because fatigue can knock several reps off your performance and drag the estimate down with them, leaving you training too light for weeks.
Treat the result as a planning number, not a promise — for sets of 2–10 reps it usually lands within about 5% of a true tested max, which is close enough to programme from safely.
Next time you finish a hard set, note the weight and reps, then put them into the One Rep Max Calculator. You will have your estimated max and a full percentage table — no risky max attempt required.