Strengthara

1RM calculator

Estimate your one-rep max from one set of 1–10 reps. Compare three formulas, add reps in reserve and work in kg or lb.

Written by Strengthara (Zenta AB) · Updated

RIR means the extra clean reps you could have done. Leave blank for 0. Completed reps plus RIR must be 10 or fewer.

Result

Enter your set and calculate. The sample fields show 80 kg for 5 reps.

Your 1RM is the most weight you can lift once in an exercise. Use the weight and reps from a single set, not the sum of several sets. These equations describe sets taken to fatigue; they do not account for technique, tempo or how you feel today.

Adding RIR treats your set as if you had completed those extra reps. That is an assumption based on your own judgment, not a separately validated formula. More uncertainty in RIR means more uncertainty in the result.

Plate loading

Choose a total weight, including the bar. Load the same plates on each side.

Assumes an unlimited supply of standard plates, largest first. kg: 25 · 20 · 15 · 10 · 5 · 2.5 · 1.25. lb: 45 · 35 · 25 · 10 · 5 · 2.5. Collars are not included.

Keep the sets you actually lift

Strengthara lets you log sets, reps and weights in the iPhone app and plan training on the web. This calculator is a separate web tool. The app does not calculate your 1RM or prescribe training weights.

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Method

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We use r = completed reps + RIR and w = weight in your selected unit. Results keep full precision for the percentage table and display one decimal. Inputs accept a comma or decimal point. The limit is 10 effective reps; it is a scope limit, not an accuracy guarantee.

Epley: w × (1 + r / 30). The 1985 equation is reproduced in the 2016 review below. Worked example: 80 kg × 5 gives 93.3 kg, matching the rounded 93 kg example published by Styrkelabbet.

Brzycki (1993): w × 36 / (37 − r). We use the fractional form rather than rounded decimal coefficients. The published example of 150 lb for 10 reps gives 200 lb.

Lombardi (1989): w × r^0.10, reproduced in the 2016 review. For example, 100 kg for 10 reps gives 125.9 kg.

For one completed rep and zero RIR, all three results equal the lifted weight. This explicitly overrides the Epley equation at r = 1. The plate tool rounds down to equal pairs on a 20 kg or 45 lb bar.

Sources

  1. Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue (1993)

    Matt Brzycki · JOPERDAccessed

  2. Strategies for maximizing power and strength gains in isoinertial resistance training (2016)

    Sakamoto, Sinclair & Naito · JPFSMAccessed