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Training · free tool

1RM Calculator

An estimated one-rep max from a set you have already done, plus the percentages to program from.

Your details

Members only — everyone else, type it in below.

Only used to label the result. The maths is the same for every lift.

The box stops at 12 on purpose — past that the estimate inflates enough to invent a lift you have never done.

Your result

An estimated one-rep max from a set you have already done, plus the percentages to program from. Fill in the boxes and press Calculate — nothing is sent anywhere and no account is needed.

How this is worked out
  1. Epley: estimated 1RM = weight × (1 + reps ÷ 30).
  2. Only applied to 12 reps or fewer. Past that it inflates enough to manufacture a maximum that was never lifted.
  3. The percentage table is straight multiplication of that estimate. The rep guides beside it are the conventional ones and hold best between 75% and 95%.

Sources

  • Epley (1985), the estimation this app already uses to award an estimated-1RM personal record from a logged set.

These are population equations. They describe averages well and individuals only roughly — which is what makes them a starting point rather than a prescription. Nothing here is medical advice.

The thinking

Why the estimate degrades with reps

Why the estimate degrades with reps

Every rep-max formula assumes a tidy relationship between how heavy a weight is and how many times you can lift it. That relationship holds reasonably well up to about eight reps and then starts to describe something else — your conditioning, your technique under fatigue, and how much discomfort you are prepared to accept.

Two people with identical maximums can differ by four or five reps at 75%. So take the estimate as a programming aid, not a fact about your body.

The same formula the app uses

This is the identical calculation Iron Katia's workout logger runs when it awards an estimated-1RM personal record from a logged set. That is deliberate: a calculator that disagreed with the app would tell a client they had set a record the app had not given them.

Questions

Straight answers.

Which formula is this?
Epley — weight × (1 + reps ÷ 30). Brzycki, Lombardi and others exist and give slightly different answers; all of them are estimates, and the differences are smaller than the day-to-day variation in what you can actually lift.
Should I test my real one-rep max?
Rarely, and not to satisfy a calculator. Testing is a skill and a risk, and most people make more progress programming from an estimate than they lose by never testing.
Why does it stop at twelve reps?
Because past that the estimate inflates enough to be misleading. If your only set is fifteen reps, the honest answer is that the formula cannot tell you.

Keep going

One number is a reading. A trend is progress.

Every calculator here gives you a starting point and nothing more. What turns it into something useful is logging what you actually do against it — which is free, takes a minute a day, and is where the 14-day START HERE challenge begins.

Start free

No card, no plan. Or see what coaching adds.

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