What a one rep max is
Your one rep max is the heaviest weight you can lift once with good form. Testing it is tiring and a little risky, so most lifters estimate it from a set they have already done. Every training percentage — the 5×5, the heavy triple, the back-off set — is a share of that number.
Formulas
Epley: 1RM = weight × (1 + reps ÷ 30)Brzycki: 1RM = weight × 36 ÷ (37 − reps)Lombardi: 1RM = weight × reps^0.10
Worked example
Five reps at 80 kg gives an estimated max of 93 kg by Epley. That makes a heavy triple about 84 kg, a working set of five about 79 kg and a set of eight about 70 kg.
How to use the 1RM calculator
- Use a real set — one you finished with clean form, not one you grinded out.
- Keep the reps low. Estimates from sets under about six reps are much closer than estimates from fifteen.
- Read the percentage table to set your working weights for the next few weeks.
Worth knowing
- Different formulas disagree by a few kilos. Pick one and stay with it so your numbers stay comparable.
- Estimates work well for compound lifts like the squat, bench and deadlift, and less well for small isolation movements.
- Warm up properly and use a spotter or safety bars before testing anything near your max.
Frequently asked questions
How accurate is a one rep max estimate?
Within a few per cent when it comes from a set of 2 to 6 reps taken close to failure. The further past six reps you go, the more the estimate overshoots.
Which 1RM formula is best?
Epley is the usual default and works well in the low rep ranges. Brzycki gives slightly lower numbers and is not reliable above 12 reps. The difference matters less than using the same one each time.
How often should I test my max?
Most lifters estimate it every few weeks from their working sets and test for real only a couple of times a year, usually at the end of a training block.