free strength calculator

one-rep max calculator.

Estimate your one-repetition maximum from a completed set of 1–10 clean reps, then see practical percentage-based weights in pounds or kilograms.

Updated September 5, 2026 · Calculations stay in your browser

estimate your 1RM

Enter the weight and number of reps from one completed set. Lower-rep sets generally produce a more useful estimate.

estimated 1RM 253 lb Brzycki estimate, not a guaranteed lift
Training weights by percentage of estimated one-rep max
PercentWeight

what a one-rep max estimate means.

A one-rep max—or 1RM—is the greatest weight you can complete for one repetition of a specific exercise with acceptable technique. An estimated 1RM uses a submaximal set instead of requiring a true maximum attempt.

This calculator uses the Brzycki equation:

estimated 1RM = weight × 36 ÷ (37 − reps)

For example, 225 lb completed for 5 reps produces an estimated 1RM of about 253 lb. The formula was published by Matt Brzycki in 1993 in Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. View the publication record.

how to get a more useful estimate.

  1. Use a set from the same exercise you want to estimate.
  2. Enter only clean, completed repetitions from one set—not the total across multiple sets.
  3. Prefer a challenging set of roughly 2–6 reps. Estimates generally become less dependable as repetitions rise.
  4. Compare estimates over time under similar conditions instead of treating one result as an absolute limit.
Training note: An equation cannot account for technique, fatigue, pain, equipment, or individual differences. Do not attempt an unfamiliar maximal lift solely because a calculator produced a number. Use appropriate safety equipment and qualified coaching when needed.

one-rep max calculator FAQ.

What is a one-rep max?

A one-rep max is the greatest weight a person can complete for one repetition of a particular exercise with acceptable technique.

How does this calculator work?

It applies the Brzycki equation to the weight and repetitions entered, then multiplies the estimate by common percentages from 50% to 100%.

Is an estimated 1RM exact?

No. It is a mathematical estimate. Exercise selection, fatigue, technique, training experience, and proximity to maximal effort can all change the relationship between a working set and a true 1RM.

Should I use pounds or kilograms?

Either works. The equation scales with the entered weight, so simply keep the same unit when reading the result.

load the estimated weight.

Once you have a target, use the barbell plate calculator to find the plates needed on each side of the bar, or the warm-up set calculator to ramp up to it. If you rate your sets by effort, the RPE calculator gives a second estimate to compare.