Which formula should I trust?

For squats and bench press, Brzycki and Epley agree within 1–2% for sets of 1–6 reps. Epley tends to overestimate slightly past 8 reps; Brzycki underestimates past 10. The average of all four is a robust compromise.

How many reps should I use in the test set?

3–6 reps to true failure gives the most accurate 1RM estimate. Sets of 10+ rely on endurance and can be off by 5–10%.

Is it safe to attempt my calculated 1RM?

Only with proper warm-up, spotters or safety pins, and a movement you can perform with strict form. Most lifters cap training intensity at 85–92% of 1RM and only test true singles in competition.

Why does the percentage table use Epley?

Epley is the simplest and most cited formula in NSCA materials, and it produces clean percentages that match the standard reps-per-percent reference table.

Does this work for every lift?

It works best for compound barbell lifts (squat, bench, deadlift, overhead press). For isolation lifts and machines, the percentage drop-off across reps is steeper and the estimate will read high.

One Rep Max Calculator

Estimate your 1RM from a working set using Epley, Brzycki, Lombardi, and O'Conner formulas.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this one rep max calculator

Pick your weight unit — kg or lb. Switching converts any value you already typed.
Enter the weight you lifted on the working set.
Enter the number of clean reps you completed (1–15 for best accuracy).
Click Calculate to compare four research-grade 1RM formulas and see the training-percentage table.
Copy the result for your training log or Reset to test another set.

About this one rep max calculator

The One Rep Max Calculator estimates the heaviest weight you could lift for a single repetition from a submaximal set, using four published formulas side-by-side: Epley 1RM = weight × (1 + reps / 30), Brzycki 1RM = weight × 36 / (37 − reps), Lombardi 1RM = weight × reps^0.10, and O’Conner 1RM = weight × (1 + 0.025 × reps). These formulas have stood up well in resistance-training literature for sets of 1–10 reps; accuracy drops past 10–15 reps because endurance becomes the limiting factor. As a worked example, lifting 80 kg for 5 clean reps gives Epley = 93.3 kg, Brzycki = 90.0 kg, Lombardi = 92.6 kg, O’Conner = 90.0 kg — an average of about 91.5 kg. The Epley value drives the training-percentage table below the result, listing the weight to use for sets at 65% (≈ 15 reps) up to 100% (1 rep). This tool is for general fitness education and is not medical advice — consult a qualified strength professional before attempting heavy singles, especially with prior injuries or untrained technique.

FAQ

Which formula should I trust?: For squats and bench press, Brzycki and Epley agree within 1–2% for sets of 1–6 reps. Epley tends to overestimate slightly past 8 reps; Brzycki underestimates past 10. The average of all four is a robust compromise.
How many reps should I use in the test set?: 3–6 reps to true failure gives the most accurate 1RM estimate. Sets of 10+ rely on endurance and can be off by 5–10%.
Is it safe to attempt my calculated 1RM?: Only with proper warm-up, spotters or safety pins, and a movement you can perform with strict form. Most lifters cap training intensity at 85–92% of 1RM and only test true singles in competition.
Why does the percentage table use Epley?: Epley is the simplest and most cited formula in NSCA materials, and it produces clean percentages that match the standard reps-per-percent reference table.
Does this work for every lift?: It works best for compound barbell lifts (squat, bench, deadlift, overhead press). For isolation lifts and machines, the percentage drop-off across reps is steeper and the estimate will read high.