How accurate are 1RM estimates?

Estimates are most accurate at low rep counts, typically one to six reps. Above ten reps the formulas diverge and overestimate, because endurance and technique increasingly affect how many reps you can grind out.

Which 1RM formula is best?

Epley and Brzycki are the most widely used and agree closely at moderate reps. Brzycki tends to read slightly lower at high reps, Epley slightly higher. Lombardi and O'Connor are alternatives; comparing all four gives a useful range.

What are the formulas?

Epley uses weight times one plus reps over thirty. Brzycki uses weight times thirty-six over thirty-seven minus reps. Lombardi uses weight times reps to the power 0.1. O'Connor uses weight times one plus reps over forty.

Does a single rep give a 1RM?

Yes. If you enter one rep, every formula returns the weight itself, because a true single is already your one-rep max for that day. The formulas only estimate beyond a single rep.

Should I test my actual 1RM instead?

Estimating is safer and avoids the fatigue and injury risk of true max attempts. Many programs base training percentages on an estimated 1RM and only test a real max during a planned peak.

Powerlifting One-Rep Max Calculator

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Find your max without risking a max attempt

Knowing your one-rep max (1RM) drives almost every percentage-based training program, but actually testing a true single is fatiguing and carries injury risk. Instead you can estimate it from a submaximal set you already performed. This calculator runs four established formulas at once so you can see both a best estimate and the spread between models.

How it works

Each formula maps the weight you lifted and the reps you completed onto a predicted single. The four implemented here are:

Epley     : 1RM = weight × (1 + reps / 30)
Brzycki   : 1RM = weight × 36 / (37 − reps)
Lombardi  : 1RM = weight × reps^0.1
O'Connor  : 1RM = weight × (1 + reps / 40)

At one rep, every formula returns the weight unchanged. As reps rise, Epley and O’Connor scale roughly linearly, Brzycki rises faster and is undefined at 37 reps, and Lombardi uses a gentle power curve. The tool also reports the average of the four as a balanced estimate.

Tips and example

Suppose you completed 100 kg for 5 reps. Epley gives 116.7 kg, Brzycki gives 112.5 kg, Lombardi gives 117.5 kg, and O’Connor gives 112.5 kg — an average near 114.8 kg. That tight cluster tells you your true single is very likely in the mid-110s.

Notes: keep the rep count honest — count only clean reps taken close to failure. For powerlifting, prefer sets of 1 to 5 reps for the most reliable estimate. Treat the average as a planning number and verify with a real top single only during a deliberate peaking block.