One Rep Max Calculator

What a one-rep max means

A one-rep max, usually written 1RM, is the heaviest weight you can lift once with good form. It is the reference point for percentage-based training: a program that asks for 80% of your max assumes you know what your max is, and getting that number badly wrong means the whole block is either too easy to drive adaptation or too heavy to recover from.

Testing a true 1RM is demanding and carries real injury risk, especially for anyone new to lifting or without a spotter. Estimation from a set of 3 to 8 reps is accurate enough to program with, and it can be repeated every few weeks without the fatigue cost of a maximal attempt.

How the estimate is calculated

This page averages three published formulas. Epley calculates weight x (1 + reps / 30). Brzycki uses weight x 36 / (37 - reps), and Lombardi uses weight x reps^0.10. All three converge closely at low repetitions and drift apart above about ten, which is why the average is shown alongside the individual estimates rather than hiding them.

Epley and Brzycki both tend to overestimate above 12 to 15 reps, and the page applies a guard there so a set of 20 does not produce a fantasy number. If your set was above 10 reps, treat the estimate as a rough ceiling and retest with a heavier set of 3 to 5.

Reading your result

The first row is the average of the three formulas, and the three rows below show each one separately so you can see the spread. A 10 kg difference between Epley and Brzycki on a heavy set is normal, not a bug: the formulas disagree most in the middle rep ranges.

The last three rows convert the estimate into working loads for 5, 8 and 12 reps, which is the part most people actually use. If the estimated 1RM is 117 kg, then 5 reps at about 102 kg, 8 reps at 94 kg and 12 reps at 82 kg all correspond to roughly the same effort - useful when a program specifies a rep target rather than a percentage.

Estimating versus testing

A tested max is the truth, but it costs a taper, a peak and a day of recovery to produce. An estimated max needs nothing more than a set you already did. For programming purposes the difference matters far less than people assume, because training loads are prescribed in ranges rather than exact percentages and because daily readiness moves performance by more than the estimate error does.

If you do test, work up in small jumps with at least three minutes of rest between attempts, keep the rep speed high, and stop the session if form breaks down. A missed attempt that turns into a grind is a failed test and a recovery debt, not a training stimulus.

Using percentages in a program

Most strength programs are written as percentages of 1RM. A simple and durable structure: work at 85% to 93% for sets of 3 to 5 when the goal is maximal strength, 70% to 80% for sets of 8 to 12 when the goal is muscle size, and 60% to 70% for volume and technique work.

Recheck the estimate every four to six weeks during a strength block, and after any layoff. Loads that were prescribed from a stale max are one of the most common reasons a program stops producing progress: the percentages look right but the absolute weights no longer match your current capacity.

Staying safe

Estimation is safer than testing, and both are safer with a spotter or safety pins. Use a rack with the pins set just below your bottom position for any heavy squat or bench set, and do not attempt a maximal single after a long layoff or while fatigued.

• Warm up with progressively heavier sets before anything near a max.
• Keep a rep or two in reserve on all sets except a planned test.
• Stop when form breaks, not when the target rep count is reached.
• Recheck the estimate after a layoff before loading heavy again.

Frequently asked questions