What is a one rep max (1RM)?
A one rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with good form. It's the gold-standard measure of absolute strength in powerlifting and strength training.
OConner Formula 1RM Calculator
The O'Conner formula is a simplified linear model that tends to give slightly more conservative 1RM estimates than Epley.
w × (1 + r/40) — The O'Conner formula is a simplified linear model that tends to give slightly more conservative 1RM estimates than Epley.
5 reps
One Rep Max
5 reps @ 225lb
253
lb
OConner formula
Big Four Strength Standards
Strength levels for a 200lb male, age 30 lifting 253lb in each lift type · enter your details.
Rep Max Projections
OConner algorithm
| Reps | Weight (lb) |
|---|---|
| 1RM | 253lb |
| 2RM | 241lb |
| 3RM | 235lb |
| 4RM | 230lb |
| 5RM(current) | 225lb |
| 6RM | 220lb |
| 7RM | 215lb |
| 8RM | 211lb |
| 9RM | 207lb |
| 10RM | 202lb |
| 20RM | 169lb |
Percentage Calculator
Based on 253lb estimated max
| Intensity | Weight (lb) |
|---|---|
| 100% | 253lb |
| 95% | 240lb |
| 90% | 228lb |
| 85% | 215lb |
| 80% | 202lb |
| 75% | 190lb |
| 70% | 177lb |
| 65% | 164lb |
| 60% | 152lb |
| 55% | 139lb |
| 50% | 127lb |
One Rep Max Calculator FAQ
Which 1RM formula is most accurate?
No single formula is universally most accurate — accuracy depends on the individual and rep range. Brzycki is considered most reliable for lower rep ranges (1–6 reps). Epley is widely cited in research. This calculator shows all 7 formulas side by side so you can see the full range of estimates.
How many reps should I use to estimate my 1RM?
Sets of 3–10 reps give the most reliable 1RM estimates. Below 3 reps you're already near your max. Above 10 reps, fatigue factors make estimates less accurate. A set of 5 reps is a common sweet spot.
What is an E1RM (estimated one rep max)?
An E1RM is a calculated estimate of your one rep max based on a submaximal set — for example, the weight you lifted for 5 reps. E1RM formulas let you track strength progress without the risk of actual max testing every session.
Can I use this calculator for squat, bench press, and deadlift?
Yes. This 1RM calculator works for any barbell lift — back squat, bench press, deadlift, strict press, and more. Enter your working weight and rep count and the calculator estimates your max across all 7 formulas.
