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One-Rep Max (Average) Calculator

Get a balanced 1RM estimate from four proven strength formulas.

How it is calculated

From one set you did (weight w and repetitions r) the tool estimates your one-rep max with four formulas and averages them: Epley w × (1 + r/30), Brzycki 36w / (37 − r), Lombardi w × r0.10 and Lander 100w / (101.3 − 2.67123 × r). The result is (Epley + Brzycki + Lombardi + Lander) / 4, shown to two decimals together with the Epley and Brzycki values. The answer is in the same unit as the weight you typed; no unit conversion is done. Reps must be between 1 and 20 and the weight above zero, otherwise there is no result. At exactly 1 rep the tool simply returns the weight you lifted, since that already is a one-rep max. The formulas assume a set taken to or very near failure, and the estimate gets less reliable as reps go up.

Worked example

You lifted 100 for 5 reps. Epley: 100 × (1 + 5/30) = 116.67. Brzycki: 3,600 / 32 = 112.50. Lombardi: 100 × 50.10 = 117.46. Lander: 10,000 / (101.3 − 13.356) = 113.71. Average: (116.67 + 112.50 + 117.46 + 113.71) / 4 = 115.08. The tool shows an estimated 1RM of 115.08, with Epley at 116.67 and Brzycki at 112.50. The spread of about 5 between the formulas is normal at 5 reps, and averaging smooths it.

Try this example →

Common mistakes

  • Entering a set you stopped well before failure, such as an easy 5 with 5 more in reserve. The formulas assume a hard set, so the estimate will be too low.
  • Using a high-rep set, for example 18 or 20. The four formulas disagree strongly there (for 100 × 20, Epley gives 166.67 and Brzycki 211.76), so the average is rough; a set of 3 to 8 reps is more reliable.
  • Mixing units, such as entering kilograms and reading the answer as pounds. The result is in whatever unit you typed.
  • Expecting a result for more than 20 reps. A set of 21 or more shows nothing, so for long sets use a heavier test set instead.
  • Counting sloppy or partial reps. Only reps done with full range and the same form as a true max attempt should be counted, and the result is a prediction to test with caution and a spotter, not a guaranteed max.

About this calculator

A one-rep max (1RM) is the heaviest weight you can lift for a single complete repetition, but testing it directly is risky and impractical for most training days, so strength coaches estimate it from a lighter set taken to near-failure using regression formulas built from decades of lifting data. The four most established are the Epley formula (1RM = weight × (1 + reps/30)), the Brzycki formula (1RM = weight × 36/(37 − reps)), the Lombardi formula (1RM = weight × reps^0.10), and the Lander formula (1RM = 100 × weight / (101.3 − 2.67123 × reps)) — each derived from different populations and rep ranges, which is why they can disagree by a few percent on the same set. All four hold only for low-rep sets — Brzycki's in particular breaks down as reps approach 37 — so the calculator accepts 1 to 20 reps.

Because no single formula is universally most accurate across all rep ranges and lifters, averaging all four gives a more balanced, less formula-dependent estimate — a practice strength and conditioning coaches use when programming percentage-based training (like 5/3/1 or linear periodization) without requiring an athlete to actually max out and risk injury or excessive fatigue.

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