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One-Rep Max (Lander) Calculator

Enter the weight and reps to estimate your one-rep max.

How it is calculated

The tool applies the Lander equation: 1RM = 100 × w / (101.3 - 2.67123 × r), where w is the weight lifted (the result is labelled in kg, so use kilograms) and r is the number of repetitions completed in the set. The more reps you did, the smaller the denominator and the larger the estimate. Reps must be between 1 and 20; outside that range the tool returns no result, because the formula becomes unreliable and eventually diverges at high rep counts. The result is rounded to two decimals. Fractional reps are accepted. It is an estimate for a set taken close to failure, not a measured max.

Worked example

You lift 80 kg for 5 reps. Denominator: 101.3 - 2.67123 × 5 = 101.3 - 13.35615 = 87.94385. Numerator: 100 × 80 = 8,000. Divide: 8,000 / 87.94385 = 90.97 kg. So the estimated single-rep maximum is about 91 kg, around 14% above the weight you used. Entering 1 rep with the same 80 kg gives 81.11 kg, slightly above the lifted weight, which shows the formula's small built-in bias.

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Common mistakes

  • Entering a set that stopped far from failure. If you could have done 12 reps but stopped at 5, the estimate comes out too low.
  • Using a very high rep set, such as 20 reps. The formula is least trustworthy at the top of its range, so prefer sets of about 3 to 10 reps.
  • Entering pounds and reading the answer as pounds. The output is labelled kg, and the formula itself does not convert units.
  • Treating the result as a safe weight to attempt. It is a prediction and different formulas (Epley, Brzycki) give different values for the same set.
  • Entering a negative or zero weight. The tool does not reject it in a helpful way, so enter the real bar load.

About this calculator

The Lander formula estimates a lifter's one-rep max (1RM) — the heaviest weight they could lift for a single rep — from a set taken to or near failure at a higher rep count: 1RM = (100 × weight) / (101.3 − 2.67123 × reps). It's one of several competing 1RM formulas (alongside Epley and Brzycki), and tends to track slightly differently at higher rep ranges than those alternatives.

Strength coaches and lifters use estimated 1RM to program training loads as a percentage of max without needing to actually attempt a risky single-rep maximum lift, and to track strength progress over time from ordinary training sets.

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Comments (1)

  • Editorial team

    Once you have an estimate, it becomes a planning number. With 100 kg for 5 reps the tool gives 113.71 kg, so 80% of that is about 91 kg. The same lift taken for 3 reps gives 107.20 kg, so estimates depend on the rep count; compare like with like by always testing with a similar set. Treat it as a guide, since fatigue, form and technique all shift it. What rep range do you usually test, and which formula have you compared it with?

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