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One Rep Max Calculator
Estimate 1RM strength from reps and load using Epley, Brzycki, Lombardi and other formulas. No signup — your inputs stay in your browser.
Step By Step
How to Use This Calculator
4 steps
- Enter the weight you lifted in your working set. Use the unit toggle (kg / lbs).
- Enter the number of clean reps you completed in that set — ideally 2–10 for best accuracy.
- Choose your preferred formula from the drop-down, or leave it on Epley for the most widely used estimate.
- Check the formula comparison table to see how different equations range and use the average as a conservative estimate.
Worked Example
Example: 90 kg lifted for 5 reps
Use this sample to sanity-check your inputs and understand what the final result represents.
- 1Epley: 90 × (1 + 5 / 30) = 90 × 1.167 = 105.0 kg
- 2Brzycki: 90 / (1.0278 − 0.0278 × 5) = 90 / 0.888 = 101.4 kg
- 3Average of 6 formulas ≈ 103 kg
- 480% of 1RM target: 82–84 kg for hypertrophy work
Final Result
Estimated 1RM ≈ 101–105 kg. Use 80% (≈ 82 kg) for 3×8 hypertrophy sets.
Methodology
Epley (1985) and Brzycki (1993) — most widely cited
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
Epley: 1RM = w × (1 + r/30). Brzycki: 1RM = w / (1.0278 − 0.0278 × r). Lombardi: 1RM = w × r^0.10. O'Conner: 1RM = w × (1 + 0.025 × r). Mayhew et al.: 1RM = 100w / (52.2 + 41.9 × e^(−0.055r)). Wathan: 1RM = 100w / (48.8 + 53.8 × e^(−0.075r)). Where w = load used, r = reps to near-failure. Accuracy is best for r = 2–10.
Frequently Asked Questions
What is a one-rep max (1RM)?+
A one-rep max is the maximum weight you can lift for a single complete repetition with proper form in a given exercise. It is the standard measure of maximal strength in resistance training, used to prescribe training loads as a percentage of 1RM. Directly testing a 1RM requires a warm-up progression and carries a small injury risk, so the estimated 1RM from a submaximal set is a safer and widely used alternative.
Which formula is most accurate?+
No single formula is universally most accurate — accuracy depends on the rep range and the individual. The Epley formula (1985, published in Athletic Journal) is the most widely cited in peer-reviewed literature. Brzycki (1993, Strength & Conditioning) tends to be slightly more accurate at low rep counts (1–5), while Epley performs better at moderate rep counts (6–10). For the most reliable estimate, this calculator shows results from six formulas and their average, which reduces the error from any single equation.
Why is the estimate less reliable above 10 reps?+
All 1RM estimation formulas assume a consistent linear or curvilinear relationship between load and maximum reps. Above about 10 reps, muscular endurance and local fatigue become significant factors that break this relationship. A well-trained endurance athlete might perform 20 reps at 60% 1RM while a pure strength athlete might only manage 12 — the same formulas applied to both would give very different accuracy. Most research validating 1RM formulas used sets of 2–10 reps.
How should I use my 1RM for programming?+
Strength programmes typically prescribe work sets as a percentage of 1RM. Common guidelines (NSCA, 2016) suggest 85–100% for maximal strength (1–5 reps), 67–85% for hypertrophy (6–12 reps), and 50–67% for muscular endurance (15+ reps). For example, if your estimated squat 1RM is 120 kg and your programme calls for 4 sets of 5 at 80%, you would use 96 kg per set.
Does 1RM differ between exercises?+
Yes — 1RM is specific to each lift. Your 1RM for the back squat will be different from the leg press, bench press, or deadlift. Each exercise involves different muscle groups, leverage points, and neuromuscular coordination. Always calculate and track 1RM separately for each major lift you are programming.