How to Calculate Your One-Rep Max (and Why Every Formula Disagrees)

Your one-rep max (1RM) — the most weight you can lift for a single rep — is the number nearly every strength program is built around. “Work up to 80% of your 1RM” only means something if you know what your 1RM is. But actually testing a true max is risky, fatiguing, and not something you want to do every week. The solution is estimation: lift a submaximal weight for a few reps, then use a formula to predict the single.

The idea behind every 1RM formula

All estimation formulas exploit the same observation: the more reps you can do with a weight, the lighter that weight is relative to your max. If you can grind out 5 reps at 100 kg, your single is somewhere around 113–116 kg. The formulas just disagree on the exact relationship.

Epley

1RM = weight × (1 + reps / 30)

The most widely used. At 100 kg × 5 reps: 100 × (1 + 5/30) = 116.7 kg.

Brzycki

1RM = weight × 36 / (37 − reps)

At 100 kg × 5 reps: 100 × 36 / 32 = 112.5 kg. Brzycki tends to read slightly lower than Epley in the 2–10 rep range.

Lombardi

1RM = weight × reps^0.10

A power-curve model that behaves differently at higher rep counts.

Why the formulas disagree

Each was fit to different populations and lifts. Key truths to keep in mind:

• Accuracy is best at low reps. A 2–5 rep set predicts your max far better than a 15-rep set, because high-rep performance depends heavily on conditioning and pain tolerance, not just strength.
• The lift matters. Squat and deadlift often allow more reps at a given percentage than the bench press, so a single formula can’t be perfect across all movements.
• You are an individual. Some lifters are “grinders” with high rep capacity; others are “twitchy” and fade fast. Your personal curve may sit above or below the average.

The One-Rep Max calculator shows several formulas side by side so you can see the spread rather than trusting one number. Take the average, or lean toward the more conservative estimate when programming heavy work.

Turning your 1RM into a training plan

Once you have an estimate, percentage-based programming becomes easy. A common rep-to-percentage guide:

Reps	% of 1RM
1	100%
2	95%
3	93%
5	87%
8	80%
10	75%
12	70%

So if your estimated bench 1RM is 116 kg and the program calls for 5 reps at 87%, you’d load ~101 kg. To stop doing plate arithmetic at the bar, the Barbell Plate Loading calculator tells you exactly which plates go on each side for any target weight.

Comparing lifts fairly

A 140 kg deadlift means something very different for a 60 kg lifter than for a 100 kg lifter. To compare strength across bodyweights — or track your own progress as your weight changes — the Wilks/DOTS calculator converts your lifts into a single normalised score used in powerlifting.

Frequently asked questions

How often should I retest my max? Re-estimate from a heavy set of 3–5 every few weeks. Only attempt a true single test occasionally, fully rested, with a spotter.

Which formula should I trust? For most lifters, Epley and Brzycki are both fine. Use a 3–5 rep set as input and treat the result as a planning tool, not gospel.

Can I use this for any lift? Yes, but expect bigger errors on isolation moves and very high-rep sets. Compound barbell lifts at low reps give the cleanest estimates.

Plug in your best recent set on the One-Rep Max calculator and you’ll have the anchor number your whole program needs.