What is a one rep max, and why estimate it instead of testing it?
Your one rep max is the heaviest weight you can lift once with proper form — the strength world's universal currency. Training programs are written in percentages of it ('squat 5×5 at 80%'), which means you need the number even if you never plan to max out.
Here's the useful secret: you don't have to max out. Grinding a true 1RM is taxing, technical, and the riskiest thing most lifters do all month. The relationship between reps and load is regular enough that a submaximal set — say, five clean reps at 100 kg — predicts your single with surprising accuracy. That's what this calculator does, using six published formulas at once.
The six 1RM formulas
Epley and Brzycki are the two you'll see everywhere. Epley multiplies your weight by (1 + reps ÷ 30); Brzycki divides it by (1.0278 − 0.0278 × reps). For 100 kg × 5 reps they give 116.7 kg and 112.5 kg respectively — a typical spread. Lombardi, O'Conner, Mayhew, and Wathan round out the set, each derived from different lifter populations, and the calculator shows all six plus their average so you can see the honest uncertainty band around your estimate.
One rule keeps the estimates trustworthy: stay under about 10 reps. The formulas were built on low-rep data, and beyond ten the math drifts optimistic — a set of 20 predicts a 1RM you'd have no business attempting. Reps in the 3–6 range hit the sweet spot between safety and accuracy.
Training percentages: putting your 1RM to work
The point of knowing your max is choosing every other weight intelligently. The classic prescription table:
| % of 1RM | Typical reps | Trains mostly |
|---|---|---|
| 90–100% | 1–3 | Maximal strength |
| 80–90% | 3–6 | Strength |
| 70–80% | 6–12 | Muscle growth |
| 60–70% | 12–15 | Growth and endurance |
| Below 60% | 15+ | Muscular endurance |
The boundaries blur in practice — muscle grows across a wide rep range when sets are taken close to failure — but as a load-selection map, this table has guided a century of programs.
If you do test a true max
Sometimes only the real number will do — a powerlifting meet, a program that demands it, plain curiosity. Then the rules are non-negotiable: a thorough warm-up building through progressively heavier singles, spotters or safety pins genuinely set up to catch a failure, no maxing alone, and form as the limit — the set ends when technique breaks, not when your ego does. Recovery matters too; a true max is a nervous-system event, and testing more than a few times a year mostly measures fatigue.
Fueling strength training properly helps both the test and the training around it — the protein calculator and calorie calculator cover that side of the bar.
Frequently asked questions about 1RM
What is a one-rep max (1RM)?
1RM is the heaviest weight you can lift for one repetition with good form. It is used to set training loads as percentages.
Should I test my true 1RM?
Only with proper warm-up, spotting, and experience. Submaximal formulas estimate 1RM without maximal attempts.
Which 1RM formula is best?
Epley and Brzycki are common. Formulas differ most at high rep ranges — use 1–10 reps for better estimates.
How do I use this one-rep max calculator?
Enter weight lifted and reps completed, pick a formula, and click Calculate.
Sources and further reading
- Reynolds JM et al. — Prediction of 1RM from multiple-rep tests (J Strength Cond Res, 2006)
- NSCA — Predicting a one rep max from a submaximal load
- Schoenfeld BJ et al. — Loading recommendations for muscle strength and hypertrophy (J Sports Sci, 2017)
This page is for general information only and is not coaching or medical advice. Lift with proper technique and appropriate supervision.