Calculator
One rep max calculator
Estimate your one-rep max from a set you've already done, without testing a true max. You get the Epley and Brzycki estimates and a table of training weights.
Fill in the fields and press Calculate to see your estimate.
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Your one-rep max (1RM) is the heaviest weight you could lift once with good form. You can estimate it from a harder set of a few reps: lift 100 kg for 5 reps and your estimated max is about 112.5 to 117.5 kg. The calculator above uses two standard formulas, Epley and Brzycki, shows the range between them, and turns the result into training weights so you never have to test a true max.
The formulas
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Brzycki published his equation in 1993 for predicting a max from reps to fatigue. The Epley equation, from a 1985 coaching chart, is written out in the same form in recent strength research, where both were reported to predict a squat max within a few kilograms from a 3- to 5-rep test. The two formulas agree exactly at 10 reps; below that Epley reads a little higher.
How many reps to use matters. A study of 70 adults aged 18 to 69 found prediction equations were accurate from multiple-rep tests, and concluded no more than 10 reps should be used for the estimate. The calculator accepts up to 15 but warns you above 10.
A worked example
You bench 100 kg for 5 clean reps, the last one hard:
| Formula | Working | Estimate |
|---|---|---|
| Epley | 100 × (1 + 5 ÷ 30) | 116.7 kg |
| Brzycki | 100 × 36 ÷ 32 | 112.5 kg |
| Shown as | rounded to 2.5 kg | 112.5–117.5 kg |
Training weights then come from the average, about 114.6 kg:
| % of estimated max | Weight (rounded to 2.5 kg) |
|---|---|
| 85% | 97.5 kg |
| 80% | 92.5 kg |
| 75% | 85 kg |
| 70% | 80 kg |
In pounds, the same set is 220 lb × 5, an estimated max of about 250–255 lb, rounded to the nearest 5 lb.
How to use your estimate
- Use a set taken close to failure. If you stopped with four reps left in the tank, the estimate will be low.
- Keep the reps between 3 and 8 where you can. Fewer reps are closer to a max effort; more reps add error.
- Use it to choose working weights, not to chase a number. A program that says “3 sets of 6 at 80%” needs a max to work from; this gives you one safely.
- Retest every four to eight weeks. Rising estimates are a clean way to see progressive overload working.
How your numbers compare with other men your age is covered in strength standards for men over 40.
Limitations
Both formulas assume your reps-to-failure behave like the average lifter’s. Men with more muscular endurance get overestimated; men who are strong but tire quickly get underestimated. Technique breakdown changes everything: five ugly reps don’t predict a clean single. And the estimates are for one lift on one day, so poor sleep or a long week shows up in the result.
When to see a doctor
Stop a set if you feel sharp or joint pain, and get it assessed before loading it again. If you have high blood pressure, a heart condition, or a hernia, check with your doctor before doing near-maximal sets.
Next step
An estimated max is only useful inside a plan that progresses it. If you’d like that plan written out week by week, the DIY programs use percentages like these from day one.
Questions people also ask
Should a man over 40 test his true one-rep max?
Rarely, and there's little need. An estimate from a hard set of 3–8 reps is close enough to plan training, without the injury risk and recovery cost of a true max attempt.
Why do Epley and Brzycki give different answers?
They're different curves fitted to the same idea. They match exactly at 10 reps and differ by a few percent elsewhere, so the calculator shows both as a range.
Does the calculator work for every exercise?
It works best for compound barbell and machine lifts like the squat, bench press and leg press. It's less reliable for small isolation moves and bodyweight exercises.
How often should I recalculate?
Every four to eight weeks, from a set taken close to failure with good form. If your working sets feel easier, it's time.
Sources
- Brzycki (1993), Strength testing: predicting a one-rep max from reps-to-fatigue, J Phys Educ Recreat Dance
- Macarilla et al. (2022), Accuracy of predicting one-repetition maximum from submaximal velocity in the barbell back squat and bench press, J Hum Kinet (states the Epley equation)
- Reynolds et al. (2006), Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry, J Strength Cond Res