How to Estimate Your One-Rep Max (1RM)

What a 1RM is (and why estimate it)

Your one-rep max is the heaviest weight you can move for a single clean repetition of a lift. It is the reference point strength programs are built around. Testing it for real is demanding and, without experience and a spotter, risky — so most people estimate it from a set they can safely complete for several reps instead.

The Epley formula

The most common estimate is Epley's: 1RM = weight × (1 + reps ÷ 30). Bench 80 kg for 5 reps and you get 80 × (1 + 5/30) = 80 × 1.167 ≈ 93 kg. Other formulas, such as Brzycki, use slightly different maths but land very close, so the exact one you pick matters little in practice.

Accuracy and limits

These formulas assume a roughly linear link between reps and load, which holds best at low reps. Under about 10 reps the estimate is dependable; push to 15 or 20 and it drifts, usually overestimating. Results also vary by lift and by person — some sustain more reps at a given percentage than others — so treat the number as a close guide, not gospel.

Training with percentages

Once you have a 1RM, programs prescribe loads as a percentage of it: roughly 70–85% for building strength, higher and heavier for peaking, lower for technique and volume work. Turn the estimate around and it tells you what to load for a target — 80% of a 93 kg max is about 74 kg. A lift-percentage calculator handles that reverse maths for you.

Frequently asked questions

Is it safe to test my true 1RM?

A genuine max attempt is risky without experience and a spotter. Estimating from a lighter set you can control is the safer route for most lifters.

How many reps should I use to estimate?

Under about 10 reps gives the most accurate estimate; the higher the reps, the more the formula tends to overshoot.

Which formula is best?

Epley and Brzycki both work and agree closely for low reps — use whichever your calculator offers; the difference is small.