1-Rep Max Calculator

Estimate your 1RM from a submaximal set

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition. Testing it directly is risky and time-consuming. Instead, you can estimate it from a lighter set using proven formulas. Enter your weight, reps, and optional RPE below to get an instant estimate across four validated equations.

Leave blank if you went to failure

How It Works

This calculator uses four well-validated formulas to estimate your one-rep max from a submaximal set. Each formula was developed and tested against actual 1RM tests in peer-reviewed research (LeSuer et al. 1997, n=67).

Epley multiplies weight by a factor based on reps: w × (1 + reps / 30). Brzycki uses w × 36 / (37 − reps) and is most accurate at 1–6 reps. O'Conner applies a smaller per-rep increment: w × (1 + 0.025 × reps). Lombardi uses an exponential model: w × reps^0.10.

The calculator shows estimates from all four formulas plus an average. The confidence badge indicates how reliable the estimate is: high for 1–5 reps (±2–4%), moderate for 6–10 reps (±4–7%), low for 11–15 reps (±8–15%), and unreliable above 15 reps.

Deadlift correction: All formulas underestimate deadlift by approximately 10% because of its longer range of motion and different strength curve. When you select "Deadlift" as the lift type, a 1.10× correction factor is applied automatically.

RPE adjustment: If you know the Rate of Perceived Exertion (RPE) of your set, entering it adjusts the estimate by accounting for reps in reserve. For example, 5 reps at RPE 8 (2 reps in reserve) is treated as 7 effective reps.

Training max percentages below the estimate show common working weights used in programs like Starting Strength, 5/3/1, and nSuns. Most programs use 85–90% of 1RM as a training max for autoregulated progressions.

Frequently Asked Questions

What is a 1-rep max?

A 1-rep max (1RM) is the maximum amount of weight you can lift for a single repetition in a given exercise. It is the gold standard for measuring absolute strength and is used to program training intensities.

How accurate is a 1RM calculator?

Accuracy depends on the rep range used. With 1–5 reps, estimates are within ±2–4% of a true 1RM (LeSuer et al. 1997). With 6–10 reps, accuracy drops to ±4–7%. Above 10 reps, estimates become unreliable with error margins of 8–15%.

Should I use the Epley or Brzycki formula?

Both formulas are well-validated. Epley works best in the 2–8 rep range, while Brzycki is optimized for 1–6 reps. This calculator shows estimates from all four major formulas and provides an average, so you get a balanced estimate regardless of which formula you prefer.

Why are deadlift estimates different?

All standard 1RM formulas underestimate deadlift by approximately 10% (LeSuer et al. 1997). This is because the deadlift has a longer range of motion and different strength curve compared to the squat or bench press. This calculator applies a 1.10× correction factor for deadlift estimates.

What does RPE mean on the calculator?

RPE (Rate of Perceived Exertion) on a 1–10 scale indicates how hard the set felt. RPE 10 means failure (no more reps possible), while RPE 8 means you could have done 2 more reps. Entering RPE adjusts the estimate by accounting for reps in reserve, giving you a more accurate 1RM prediction.

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