One rep max calculator

What a one rep max is, and why you should not test it

Your one rep max (1RM) is the heaviest weight you could lift once with good form. Programmes are written as percentages of it - "5 sets of 5 at 80%" - so you need a number, but actually maxing out is the riskiest thing you can do in a gym, especially as a beginner. Estimating it from a set you have already done is safer and nearly as accurate.

How the estimate works

Enter the weight and how many clean reps you got with it. The calculator runs two well-tested formulas - Epley (weight × (1 + reps ÷ 30)) and Brzycki (weight × 36 ÷ (37 − reps)) - and averages them. Both are most accurate between 2 and 6 reps; past 10 reps the estimate gets loose because endurance starts to matter more than strength. That is why the input is capped at 12.

Using the percentage table

The table gives training weights rounded to the nearest plate. Most beginners make the best progress in the 70–85% band with 5–10 reps, adding 2.5 kg when every set feels solid. Save the 90%-plus rows for when you have been lifting consistently for a few months and your technique is automatic.

Same number, different lifts

Run it separately for squat, bench, deadlift and overhead press - they do not scale together. And re-test every 4–6 weeks with a hard set of 3–5, not a single: the number will move faster than you expect at the start. Not sure what to do with these weights? Our beginner gym plan lays it out session by session.

FAQs

How accurate is a one rep max calculator?

Usually within about 5% when you use a set of 2–6 reps done to near failure. Sets of 10 or more are less reliable because they test endurance as much as strength.

Should beginners test their one rep max?

No. In your first few months technique is still settling, and a true max attempt is where injuries happen. Use a calculator from a 5-rep set instead - it gives you the same programming number without the risk.

What percentage of my max should I train at?

For building both strength and muscle, most work sits between 70% and 85% for 5–10 reps. Heavier than 90% is for experienced lifters and occasional testing.

What is a good bench press or squat for a beginner?

It depends on bodyweight and how long you have trained. Rough UK gym benchmarks after six months of consistent training are a bench around 0.75–1× bodyweight for men and 0.5× for women, and a squat around 1–1.25× bodyweight for men and 0.75× for women. The right target is simply more than last month.