Estimates your one-repetition maximum (1RM) from a lighter weight lifted for multiple reps, using the widely used Epley formula.
How it works
The weight lifted is multiplied by one plus the rep count divided by 30 to estimate the maximum weight liftable for a single rep.
What this does not include
This is an estimate, not a guarantee — actual 1RM depends on factors like lift technique, fatigue, and individual strength-endurance profile, and different estimation formulas (like Brzycki) can diverge more at higher rep counts.
How to use this calculator
- Enter the weight you lifted and how many reps you completed.
A worked example
135 lb for 5 reps → 135 × (1 + 5/30) = 157.5 lb estimated 1RM.
225 lb for 3 reps → 225 × (1 + 3/30) = 247.5 lb estimated 1RM.
What the variables mean
| Variable | Meaning |
|---|---|
| Weight lifted | The load used for the set |
| Reps completed | How many reps were done at that weight (capped around 15 for reliability) |
Edge cases worth knowing
The Epley formula gets less reliable at higher rep counts. Beyond roughly 10–15 reps, a set is testing muscular endurance more than maximal strength, and the estimate drifts further from an actual tested 1RM.
Different estimation formulas (like Brzycki) can diverge noticeably at higher reps — this calculator’s Epley-based estimate is one widely used method, not the only one in use.
Frequently asked questions
Why estimate 1RM instead of testing it directly?
Testing a true 1RM carries injury risk and requires significant warm-up and recovery — estimating from a lighter, higher-rep set is safer for regular training use.
How accurate is the Epley formula?
It’s reasonably accurate for lower rep ranges (around 1-10 reps) but becomes less reliable as rep count increases, since fatigue and endurance start to matter more than pure strength.
Why does this cap at 15 reps?
Beyond that range, rep-based 1RM estimation formulas generally become unreliable, since the set is testing muscular endurance more than maximal strength.
