One-rep max calculator (kg)

Enter a set you actually did and get an estimated one-rep max, plus the working weights that sit under it. Kilograms first, Epley formula, no sign-up.

The formula

1RM = weight × (1 + reps ÷ 30)

So 100 kg for 5 reps gives 100 × (1 + 5 ÷ 30) ≈ 116.7 kg. The estimate is most useful between 1 and 10 reps. This is general training information, not medical advice.

Not sure how hard a set was? Here's how to log RPE.

New to keeping a log? Here's what to write in a gym diary.

Questions people ask

What is a one-rep max?

Your one-rep max (1RM) is the heaviest weight you could lift once with good technique on a given exercise. Most people estimate it from a heavier set rather than actually testing a single.

Is the Epley formula accurate?

It is a good estimate in the 1–10 rep range and gets less reliable as reps climb. Above about 10 reps, fatigue and technique drift matter more than the maths, so treat the number as a planning tool rather than a measurement.

Why does this calculator use kilograms?

Twaka is built in Australia, so kilograms are the default. The formula is unit-agnostic: enter pounds and the estimate comes back in pounds.

How do I use a 1RM for programming?

Pick a percentage band for the job: roughly 85–95% for heavy strength work, 70–85% for most working sets, and 60–70% for technique or volume days. Recalculate every few weeks from a recent hard set.

Should I test a true single instead?

Only if your sport requires it and you are well warmed up with someone spotting. An estimate from a set of 3–5 is far less risky and usually close enough for planning.