One rep max calculator

You do not need to attempt a true maximum to know roughly where it sits — a hard set of five will tell you.

Why estimate rather than test

A true one rep max is useful but expensive. It demands a full warm-up, carries the highest injury risk of anything in the gym, needs a spotter on most lifts, and leaves fatigue that can cost several days of training. Estimating from a hard set of three to six gives a number within a few percent for most people, at almost no cost.

The two formulas

Epley (1985) — 1RM = w × (1 + r/30)
Brzycki (1993) — 1RM = w × 36 / (37 − r)

They agree closely at 10 reps and diverge either side. Below 10, Brzycki predicts slightly higher; above 10, Epley does. Neither is more correct in general, which is why the average is offered — for a set of five they typically sit within 1-2% of each other, and the disagreement itself is a useful honesty check.

Note that Brzycki breaks down completely at 37 reps, where the denominator hits zero. That is a clue about the real limitation: these are linear approximations of a relationship that is not linear, fitted over a modest range.

Reps in reserve changes everything

Every one of these formulas assumes the set was taken to genuine failure, or within a rep of it. If you stopped with three reps left in the tank, the estimate is badly low — potentially by 10% or more.

Be honest about the set you actually did. A useful test: if you could have done another rep with good form, add it to the count before calculating, or accept that the number is conservative. Most people overestimate how close to failure they train.

Using the percentage table

The table below the result is where the number earns its keep. Most programmes prescribe load as a percentage of 1RM — 5 × 5 at 80%, or singles at 90% — and having those figures computed removes a source of arithmetic error at exactly the moment you least want one.

Round to what your gym actually has. If the smallest plates are 1.25 kg a side, rounding to 2.5 kg is realistic and the rounding option handles it.

Where the estimate is least reliable

Accuracy is best on compound barbell lifts with a stable groove — squat, bench, deadlift, overhead press. It is poor on isolation movements, on machines with unusual strength curves, and on anything limited by grip or balance rather than by the target muscle. Deadlift 1RMs in particular tend to be overestimated from high-rep sets, because grip and lower back endurance fail before peak force does.

Common questions

How many reps give the most accurate estimate?

Three to six. Below three there is little to extrapolate from; above ten, endurance and technique start limiting the set instead of peak strength, and the formulas drift apart noticeably.

Which formula should I use, Epley or Brzycki?

Either — they agree at 10 reps and differ by only 1-2% at five. Brzycki reads slightly higher below 10 reps, Epley slightly higher above. If they disagree meaningfully, that itself tells you the rep count is too high to extrapolate from.

Does the set have to be taken to failure?

Effectively yes. These formulas assume you stopped at or within one rep of failure. Stopping with three reps in reserve can understate your maximum by 10% or more.

Is an estimated 1RM safe to use for programming?

Yes, and it is safer than testing a true max. Use it to set percentages, then adjust from how the working sets actually feel. Re-estimate every few weeks rather than testing.