One Rep Max Calculator

You worked out one number from one set. THYMOS estimates this from every set you log, keeps both formulas straight, and shows you whether the estimate is trending up or whether you just had a good day. See the THYMOS product facts and FAQ for the current feature overview.

Using it for bench press, squat and deadlift

The formulas do not know which lift you did — they take a weight and a rep count and nothing else. What changes between lifts is how much you should trust the answer.

Bench press 1RM

Bench is the lift these formulas handle best, and the one most people use them for. The range of motion is short, the bar path is consistent, and a set to technical failure on bench is easier to judge honestly than on a squat. If you benched 100 kg for 5 clean reps, your estimated max is 112.5 kg by Brzycki. Treat that as a comparison point, not as a weight to unrack next week — a true bench max needs a spotter and a different mindset.

Squat 1RM

Squat estimates tend to run high. Most people leave more reps in reserve on a squat than they think, because the set stops feeling safe well before it stops being possible, and depth quietly shallows out as fatigue builds. If your estimate looks generous, it probably is. Use a set of 3 to 5 rather than 8 to 10 and the number tightens considerably.

Deadlift 1RM

Deadlift is the least reliable of the three here. There is no eccentric to rebound from, grip often fails before the posterior chain does, and rep quality falls off a cliff rather than degrading gradually. Estimates from high-rep deadlift sets are close to meaningless. From a heavy triple they are usable.

Anything else

Overhead press, rows, curls, leg press: the same arithmetic applies. For weighted pull-ups and dips you need the total load first, which is your bodyweight plus what you added — work that out with the weighted pull-up calculator and bring the total back here.

The two formulas, in full

There is no secret here, and that is the point. Both formulas are published literature that every app in this category uses. Showing them is the difference between a tool and a slot machine.

Brzycki (1993)

Brzycki is the default. It tends to be more conservative in the low rep ranges, which is where most people actually test.

Epley (1985)

Epley climbs faster as reps rise. At one rep the two agree exactly, since both must return the weight you lifted; they diverge steadily from there.

Why this stops at 10 reps

Above roughly 10 reps these formulas stop describing strength and start describing endurance, and the error grows fast. A set of 20 says far more about your work capacity and your tolerance for discomfort than about your maximum.

So this page refuses rather than guesses. If you enter 11 or more reps you get a message, not a confident number. The THYMOS app applies the same rule internally — it is the same code path, verified against the app's own test fixtures.

What an estimate is actually worth

An estimated 1RM is not a max. It is a way of comparing today's set to last month's set on one scale. Used that way it is genuinely useful: it lets a set of 8 and a set of 3 be compared without pretending they are the same thing.

Used as a target it is a good way to get hurt. The formula does not know your sleep, your technique under a true maximum, whether you had a spotter, or whether those last two reps were clean. Treat it as a trend line, not a number to attempt.

• Use the same formula every time. Switching between Brzycki and Epley mid-programme invents progress that did not happen.
• Feed it honest reps. Reps to technical failure, not reps to grinding collapse and not reps you left three in the tank on.
• Compare like with like. An estimate from a set of 3 and one from a set of 9 carry different amounts of error.
• Round to what you can load. The percentage table gives exact arithmetic; the plate calculator tells you what your rack can actually make.

Common questions

Which formula should I pick?

Whichever one you will keep using. Consistency matters far more than the choice. If you have no preference, Brzycki is the default here.

Why is my estimate different from another site's?

Most sites average several formulas without saying which. This page shows you the arithmetic, so you can see exactly where the number came from.

Does it work for pull-ups and dips?

Not directly — you first need the total load, which is bodyweight plus what you added. Work that out with the weighted pull-up calculator, then bring the total back here.

One estimate is a data point. A hundred is a trend. THYMOS keeps the estimate on every set you log, offline, with no account and no trackers.