Estimated 1RM: three formulas, three answers

Estimated 1RM is the one number in a training log that everybody quotes and almost nobody checks. It is a projection from a submaximal set, and there are at least a dozen published ways to do it that all give different answers.

Three of them account for most of what apps actually use.

Where w is the load and r is the reps completed.

How far apart they get

Take 225 lb for 8 reps.

Eight pounds between the highest and the lowest, about 2.9%. Tolerable.

Now take 185 lb for 12 reps.

Twenty-nine pounds, about 12%. The formulas also swap order: Brzycki was the middle answer at 8 reps and the highest at 12.

That is the property worth carrying: the disagreement grows with reps, and it grows fast. All three were fitted to sets in the 1 to 10 range. Past that they are extrapolating, and they extrapolate differently.

Which one to use

Whichever you like, and then never change it.

The absolute number is not the point. Nothing in your training depends on whether your bench projects to 279 or 285 — you are not attempting either of them next Tuesday. What you care about is the direction over eight weeks, and every formula gives you the same direction from the same inputs.

What ruins that is switching. Change formula mid-block and your e1RM moves 6% overnight, which reads as a stall or a jump that never happened. Same reason you should never compare an e1RM from one app against one from another without knowing what each of them ran.

So the rule is: pick one, keep it, and expect any app you use to tell you which one it picked. An app that shows a bare e1RM without naming the formula is handing you a number you cannot compare to anything.

Where it stops meaning anything

Above about 10 reps. See the table. A 20-rep set does not project to a single, it projects to whatever the curve was doing when someone fitted it.

On isolation lifts. Nobody has a leg extension one-rep max. There is no attempt anyone makes at that movement that the projection corresponds to, the mechanics do not hold at maximal load, and the number is a decoration. Best set and volume tell you everything you actually want to know from a lateral raise.

On assisted movements. An assisted pull-up logs the assistance, so the weight moves down as you get stronger and any formula reads it backwards.

On anything where form changes with load. The formulas assume the movement you did for 8 is the movement you would do for 1. On a deadlift that is roughly true. On a barbell row it is not.

What to do with it

Track it, do not chase it. Estimated 1RM is a trend line on a compound lift, and its job is to answer “is this getting stronger over a block” in one number when the rep and load numbers are both moving and are hard to compare directly.

If you want to know your actual max, test it. If you want to know whether you are getting stronger, an e1RM from a consistent formula on a consistent movement will tell you that without a heavy single and the week it costs.

Where this comes from

The three equations are Epley (1985), Brzycki (1993) and Lombardi (1989), all still in print in every strength textbook. The reliability work on rep-max prediction — that error rises with reps and is smaller on compound movements — is reviewed by LeSuer and colleagues (1997, Journal of Strength and Conditioning Research), which compared these formulas against measured 1RMs on the bench, squat and deadlift.