One Rep Max (1RM) Calculator
Estimate your one-rep max without the risk of testing it. Enter any recent set — weight and reps — and get your 1RM by two standard formulas, plus the percentage table training programs are written in.
How to use this calculator
- Enter the weight of a recent hard set and the reps you completed.
- Sets of 3–10 reps taken close to failure give the best estimates.
- Press Calculate for your 1RM and the full %1RM loading table.
Formula used
The formulas agree closely up to ~10 reps and diverge beyond. Averaging them hedges their biases: Epley runs slightly higher at high reps, Brzycki slightly lower. All estimates assume the set approached failure.
Example calculation
80 kg × 8 reps: Epley = 80 × (1 + 8/30) = 101.3 kg; Brzycki = 80 × 36/29 = 99.3 kg → 1RM ≈ 100 kg.
Programming from that: 5×5 at 85% = 85 kg; hypertrophy sets at 75% = 75 kg.
Why train by %1RM
Strength programs prescribe loads as percentages of your one-rep max — 5×5 at 80%, heavy triples at 90% — because percentages scale to any lifter. Estimating 1RM from a rep set gives you that anchor without the injury risk and nervous-system cost of actually maxing, which is why even competitive lifters test true maxes only a few times a year.
The rep-to-percentage mapping is the useful inverse: if the program says 8 reps, that's ~80%; if it says 90%, expect ~3 hard reps. Recalculate every few weeks — a rising estimated 1RM is progress made visible.
Why use this calculator?
- Set working weights from any program's percentages without max testing.
- Track strength progress through the estimated 1RM trend.
- Convert between reps and intensity with the built-in table.
Frequently asked questions
How accurate are 1RM formulas?
Within ~5% for sets of 10 or fewer reps taken near failure, with accuracy best at 3–6 reps. Individual factors (fiber type, technique efficiency) shift results — treat the number as a working anchor, not a certified max.
Should beginners test their real 1RM?
Generally no — maximal attempts stress technique precisely when it's least stable. Estimating from 5–8 rep sets provides everything programming needs; save true max testing for experienced lifters with spotters.
How much should my 1RM increase per month?
Beginners can add 2–5% monthly on big lifts; intermediates see progress in smaller, slower waves. If the estimate stalls for 6+ weeks, look at programming, calories and sleep before adding more volume.