One-rep max calculator

Free, no sign-up, works in kilograms and pounds · Em português

Put in a weight you lifted and how many reps you managed with it. You get the load you could probably handle for a single rep, plus the percentages most training programmes are written in.

What a one-rep max actually is

Your one-rep max is the heaviest load you could lift once with good form. It is the reference nearly every strength programme is written against: when a plan says five sets of three at 85%, the 85% is 85% of this number.

Testing it for real means working up to a genuine limit single, which is tiring, needs a spotter on most lifts, and is not something to do often. Estimating it from a set you already did costs nothing and is close enough to programme with.

The formula

This page uses the Epley formula, published by Boyd Epley in 1985 and still the most widely used of the estimates:

So 100 kg for 8 reps gives 100 × (1 + 8 ÷ 30) = 126.7 kg. There is one deliberate exception: a single rep returns the weight unchanged. Epley would report 103.3 kg for a 100 kg single, but lifting a weight once already is a one-rep max of that weight, and inflating it would overstate what you actually did.

How far to trust it

The estimate is at its best between two and about six reps. In that range the set ends because the weight is heavy, which is the thing the formula is modelling.

Past ten reps it drifts, and it drifts upward. A long set ends because you ran out of breath and your grip gave up, not because the bar was close to your limit — so the formula reads endurance as strength. If you want a number worth programming with, take it from a heavy set of three to five, not from a set of fifteen.

It also varies by lift. Estimates tend to run closer on the squat and deadlift, where big muscles and a long range of motion make the reps honest, and further off on the bench press and on isolation work, where technique and leverage change more as you fatigue.

Other formulas, and why the number moves

Epley is not the only estimate. Brzycki gives weight × 36 ÷ (37 − reps), Lombardi gives weight × reps0.10, and there are a dozen more. They agree closely at low reps and spread apart as the reps climb — at three reps Epley and Brzycki are within a kilo of each other, at twelve they can be ten kilos apart.

That spread is the honest answer to how precise any of this is. Pick one and stay with it, so that when your estimate goes up it is because you got stronger and not because you changed formula.

Using the percentages

The table above is the practical part. Once you know your 1RM, the percentages tell you what to load for the work you are actually doing: heavy singles and doubles near the top, the bulk of strength work in the 80–90% band, and volume work below that.

The rep column is what the Epley formula itself implies for each percentage, rearranged. It is a starting point rather than a prescription — on any given day sleep, food and stress move it around more than most people expect.

Common questions

Does it work in pounds?

Yes. The formula multiplies whatever weight you give it, so the maths is identical in kilograms and pounds. Switch the unit and the result follows.

Should I test my real one-rep max instead?

Only if you compete, or if you are curious and have someone to spot you. For programming, an estimate from a heavy triple gets you close enough and costs you nothing in recovery.

My estimate went down. Did I get weaker?

Not necessarily. A max estimated from a set of ten on a bad day will read lower than one from a set of three on a good day, even with no change in strength. Compare like with like: same lift, similar rep range, similar conditions.