OneTaskBy Tim King · Updated
One Rep Max Calculator
Epley, Brzycki and Five More Formulas, Plus a 50% to 100% Training Chart
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How the One-Rep Max Calculator works
This one rep max calculator estimates the heaviest single lift you could manage from a set you have already done. Enter the weight and how many clean reps you got, and it shows your estimated 1RM by seven published formulas, the spread between them, and a chart of training weights from 50% to 100% of that max.
Testing a true one-rep max is tiring and carries more risk than a normal working set, so most lifters estimate it instead. A hard set of three to six reps predicts the max well, because the relationship between load and reps is close to a straight line in that range. Past ten reps, muscular endurance starts to matter as much as strength and the formulas disagree more.
How the one rep max calculator works
Each formula turns weight and reps into a predicted single. The Epley formula is 1RM = weight × (1 + reps ÷ 30); Brzycki is weight × 36 ÷ (37 − reps); Lombardi is weight × reps^0.1. Lander, O'Conner, Mayhew and Wathan are similar curves fitted to different groups of lifters. Average of all formulas takes the mean of the seven, which smooths out the quirks of any one.
First example. 100 kg for 5 reps gives 116.7 kg by Epley, 112.5 kg by Brzycki and 115.5 kg on average, so a sensible estimate is about 115 kg.
Second example. 185 lb for 8 reps on the bench gives an Epley 1RM of 185 × (1 + 8 ÷ 30) = 234 lb and a Brzycki 1RM of 185 × 36 ÷ 29 = 230 lb.
How many reps should I test for the best estimate? Three to five. The formulas agree within about 3% there, and the set is heavy enough to reflect real strength.
Estimated 1RM for a set at 100 kg (or any unit) by reps
| Reps | Epley | Brzycki | Lombardi | Mayhew | Average of 7 formulas |
|---|---|---|---|---|---|
| 1 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |
| 2 | 106.7 | 102.9 | 107.2 | 111.4 | 106.1 |
| 3 | 110.0 | 105.9 | 111.6 | 114.0 | 109.3 |
| 4 | 113.3 | 109.1 | 114.9 | 116.5 | 112.4 |
| 5 | 116.7 | 112.5 | 117.5 | 119.0 | 115.5 |
| 6 | 120.0 | 116.1 | 119.6 | 121.5 | 118.5 |
| 7 | 123.3 | 120.0 | 121.5 | 123.9 | 121.6 |
| 8 | 126.7 | 124.1 | 123.1 | 126.3 | 124.7 |
| 9 | 130.0 | 128.6 | 124.6 | 128.6 | 127.9 |
| 10 | 133.3 | 133.3 | 125.9 | 130.9 | 131.0 |
| 11 | 136.7 | 138.5 | 127.1 | 133.2 | 134.3 |
| 12 | 140.0 | 144.0 | 128.2 | 135.4 | 137.6 |
| 13 | 143.3 | 150.0 | 129.2 | 137.6 | 141.1 |
| 14 | 146.7 | 156.5 | 130.2 | 139.7 | 144.6 |
| 15 | 150.0 | 163.6 | 131.1 | 141.7 | 148.3 |
| 16 | 153.3 | 171.4 | 132.0 | 143.7 | 152.1 |
| 17 | 156.7 | 180.0 | 132.8 | 145.7 | 156.2 |
| 18 | 160.0 | 189.5 | 133.5 | 147.6 | 160.4 |
| 19 | 163.3 | 200.0 | 134.2 | 149.4 | 164.9 |
| 20 | 166.7 | 211.8 | 134.9 | 151.2 | 169.7 |
Tips and pitfalls
- Count only clean reps. A rep with a big grind, a half lockout or a spotter's help does not count, and including it inflates the estimate.
- Fresh sets predict best. Use a top set done early in the session, not the fourth set after fatigue has built up.
- Lifts differ. Lower-body lifts usually allow more reps at a given percentage than the bench press, so the same formula can overshoot a squat max.
- Estimates are not tests. Use the number to plan training percentages; save true singles for meets or planned test days.
FAQ
How accurate is a one-rep max calculator?
For sets of two to six reps, estimates usually land within about 5% of a tested max for trained lifters. Accuracy falls as reps climb, because endurance and technique under fatigue start to matter, so a set of 15 can miss by 10% or more.
Which 1RM formula is best?
No single formula wins for every lifter and lift. Epley and Brzycki are the most widely used and agree closely around five reps. Averaging several formulas, as the default setting here does, tends to cancel out the bias of any one curve.
How do I calculate my one-rep max by hand?
Use the Epley formula: multiply the weight by one plus the reps divided by 30. For 80 kg lifted 6 times, that is 80 × (1 + 6 ÷ 30) = 80 × 1.2 = 96 kg. Brzycki gives 80 × 36 ÷ 31 = 92.9 kg.
Should beginners test a true one-rep max?
Usually not. Beginners gain strength quickly from moderate weights, and a true single needs good technique and a capable spotter. Estimating from a solid set of five is safer and is accurate enough to set training weights for the first year or so.
Why does the calculator stop at 20 reps?
Above about 20 reps the formulas diverge wildly; Brzycki even heads towards infinity near 37 reps. A set that long is testing muscular endurance rather than maximal strength, so any one-rep max estimate from it would be little better than a guess.
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