One-Rep Max Calculator: Estimate Your 1RM

How to use the one-rep max calculator

1. Choose kilograms or pounds.
2. Enter the weight lifted and the number of completed repetitions.
3. Choose Brzycki, Epley, or Lombardi. Brzycki is the default.
4. Calculate to see the estimated one-rep max and percentage-based training weights.

Use a challenging set of 1 to 12 repetitions completed with consistent technique. The result is an estimate, not a tested maximum.

Methodology and formulas

The calculator applies the selected repetition-based equation and rounds the result to 0.1 kg or lb.

• Brzycki: 1RM = weight / (1.0278 - 0.0278 x repetitions)
• Epley: 1RM = weight x (1 + repetitions / 30)
• Lombardi: 1RM = weight x repetitions^0.10

Different formulas can return different estimates from the same set. Switching formulas lets you see that variation without changing the input.

Worked example

With 100 kg for 5 repetitions, the Brzycki formula estimates 112.5 kg:

100 / (1.0278 - 0.0278 x 5) = 112.5 kg

The percentage table then shows 90 kg at 80 percent of the estimate.

Using the estimate

• Use it as a repeatable reference for planning loads and tracking changes.
• Compare results for the same exercise, formula, technique, and repetition range.
• Treat the displayed percentage weights as arithmetic references, not prescribed training loads.

Assumptions and limitations

• Repetition-based formulas estimate rather than directly test a one-rep max.
• The estimate can vary with exercise, technique, range of motion, fatigue, and how close the set was to failure.
• Accuracy can decrease as the repetition count rises, so the calculator accepts no more than 12 repetitions.
• Do not attempt a maximal lift only because a calculator produced a number.