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One Rep Max Calculator
Your lift
Example: 225 lb for 5 reps — Epley 262.5 lb, Brzycki 253.1 lb, so about 253–263 lb.
Behind the numbers
How your one rep max is calculated
Your one rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is tiring and risky, so this calculator estimates it from a lighter set you already did. Enter the weight you lifted and how many reps you managed, and it applies two well-known formulas — Epley and Brzycki — then shows both answers. The two formulas rarely agree exactly, so the range between them is the honest answer: your true 1RM is probably somewhere in between. The table below the result turns your 1RM into training weights, so you can pick a load for any rep target without guessing.
Epley: 1RM = weight × (1 + reps ÷ 30). Worked example: 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb.
Brzycki: 1RM = weight × 36 ÷ (37 − reps). Worked example: 225 × 36 ÷ (37 − 5) = 225 × 36 ÷ 32 = 8100 ÷ 32 = 253.1 lb.
The percentage table uses the Brzycki curve: % of 1RM for n reps = (37 − n) ÷ 36 × 100. For 5 reps that is 32 ÷ 36 = 88.9%, and 88.9% of 253.1 lb is 225.0 lb — exactly the weight lifted, which is a good check that the table is consistent.
Training weights
Percent of 1RM for 1–12 reps
For the example above (225 lb × 5 reps, Brzycki 1RM of 253.1 lb), the weights you can expect to lift are:
| Reps | % of 1RM | Weight (lb) |
|---|---|---|
| 1 | 100.0% | 253.1 |
| 2 | 97.2% | 246.1 |
| 3 | 94.4% | 239.1 |
| 4 | 91.7% | 232.0 |
| 5 | 88.9% | 225.0 |
| 6 | 86.1% | 218.0 |
| 7 | 83.3% | 210.9 |
| 8 | 80.6% | 203.9 |
| 9 | 77.8% | 196.9 |
| 10 | 75.0% | 189.8 |
| 11 | 72.2% | 182.8 |
| 12 | 69.4% | 175.8 |
Tips before you lift
Use a set of 3 to 10 reps for the best estimate — 1-rep and 12-rep sets are the least accurate inputs.
Count only clean reps with full range of motion; a sloppy last rep inflates your estimate.
Epley usually runs a little high and Brzycki a little low, so plan training weights from the middle of the range.
Retest every 6 to 8 weeks; your 1RM moves as you get stronger, and old numbers lead to wrong training loads.
Never test a true 1RM alone — always use a spotter and safety bars on bench press and squat.
Good to know
Frequently asked questions
How accurate is a one rep max calculator?
For most lifters it lands within about 5% of a real tested max when the input set is 3 to 10 reps. It is an estimate, not a measurement — sleep, fatigue, and technique on the day all shift the real number.
Which formula is better, Epley or Brzycki?
Neither is clearly better; Epley tends to overestimate slightly and Brzycki tends to underestimate slightly, especially above 8 reps. That is why this calculator shows both — the truth is usually between them.
Can I use kilograms instead of pounds?
Yes. The formulas work in any unit, so enter your weight in kilograms and the answer comes out in kilograms. Just keep the input and the answer in the same unit.
Why does the calculator only accept 1 to 12 reps?
Both formulas were built and checked on low-rep strength sets. Past 12 reps, endurance matters more than strength and the estimates drift far from reality.