How accurate is a 1RM calculator?

1RM estimates are most accurate in the 1–10 rep range. Above 10 reps, fatigue and technique make the estimate less reliable. Use it as a training guide, not a guaranteed max.

Which 1RM formula is best?

Epley and Brzycki are the two most widely used. They agree closely at low reps and diverge slightly at higher reps. Ironside uses these same formulas to chart your estimated 1RM over time.

One-Rep Max (1RM) Calculator

Estimate your one-rep max from any weight and rep count. Free, instant, no sign-up.

Weight lifted Reps completed Unit

116 kg

Estimated one-rep max (average of Epley & Brzycki)

How it works

A one-rep max (1RM) is the most weight you can lift for a single rep. Rather than testing a true max (which is fatiguing and risky), you can estimate it from a set you already did. This calculator uses the two most trusted formulas:

Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)

Estimates are most accurate between 1 and 10 reps. Above that, treat the number as a rough guide.

Track your 1RM automatically

Ironside estimates your 1RM after every set and charts it over time for every lift, so you can see when you're progressing and when you've plateaued, without touching a calculator. It's a local-first iOS workout tracker with no subscriptions or ads.

Get Ironside on the App Store

Try the plate calculator and the training volume calculator, or read how to track your 1RM over time.

One-Rep Max (1RM) Calculator

How it works

Track your 1RM automatically

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