One Rep Max Calculator

Written by the CalculatorBoss Health Team · Checked against a reference implementation · Last updated Aug 2026

What a one rep max actually is

Your one rep max is the heaviest load you could move for a single clean repetition of a given lift. It is specific to the lift, not to you: a bench press max says nothing useful about your deadlift, and the two rarely move in step. That specificity is the first thing people get wrong about the number.

Testing a true max is a real session in its own right. It needs a full warm-up, a spotter for anything overhead or on your chest, and a day where you are fresh rather than three days into a hard week. It also leaves you flattened for a day or two afterwards. That cost is the reason estimation exists at all — coaches want the number often, and nobody wants to pay for it every time.

So the alternative is to work backwards. You take a set you already did, with a weight you could handle for a handful of reps, and you project what a single would have looked like. The projection is arithmetic, not measurement, and everything below is about how much to trust it.

The three formulas, and the arithmetic behind them

This calculator carries three published equations. Each one was fitted to a group of lifters and then written down as a formula simple enough to use at the rack, which is exactly why they disagree with each other.

Run the same set through all three and you get three answers within a few kilos of each other. Epley climbs in a straight line with reps. Brzycki has reps in the denominator, so it starts close to Epley and then pulls away, reading lower as the set gets longer. Lombardi raises reps to a small power, which flattens it out at the top end — it drops off far more gently than the other two once you are past ten.

One case is worth pointing out because it is not really a formula at all. At one rep, all three collapse to the weight you lifted. That is not a special case someone bolted on: if you lifted it once, that lift is your max for that day, and there is nothing left to extrapolate. The table on this page reflects that, showing your entered weight at one hundred percent for a single.

Which formula to pick

There is no formula that is simply correct. Each was built from a particular population, and how well it fits you depends on where you sit relative to that group. What can be said with more confidence is where each one behaves reasonably.

Epley is the one most calculators default to and the one most widely cited in research, which makes it the sensible starting point and the default here. Brzycki tends to return the more conservative number, and a conservative number is the safer one to load a bar with. Lombardi sits apart from both, and is most useful as a sanity check — if it disagrees sharply with the other two on your set, that is a signal your rep count is further out than the formulas are comfortable with.

The practical rule matters more than the choice: pick one and stay with it. If you switch formulas between training blocks, part of the change you see is the equation, not you. Consistency in the method is what makes the trend readable.

Why the rep box stops at ten

The rep field accepts one through ten, and that ceiling is deliberate rather than arbitrary. Past about ten reps a set stops being a test of strength and starts being a test of endurance, conditioning and pain tolerance. Two people with identical maxes can post very different numbers on a set of fifteen, which means the arithmetic no longer has a stable relationship to work with.

Brzycki shows the problem most starkly. Its denominator is thirty-seven minus your reps, so as reps climb toward thirty-seven the denominator heads for zero and the estimate runs away to nonsense. The formula was never intended for that territory; the cap simply keeps you out of it.

If your only recent set was a long one, the honest answer is that you should do a heavier, shorter set before trusting a projection. Three to six reps taken close to failure gives all three equations the most stable footing.

Reading the percentage table

The percentage table is the part you will actually use week to week. Once you have a max, loading is usually prescribed as a share of it rather than as an absolute weight, which is what lets one tested or estimated number program a whole block.

Broadly: the heaviest work, singles and doubles, sits up around ninety percent and above. Primary strength work tends to live in the eighty to ninety band. The range usually described as the hypertrophy zone falls around sixty-five to eighty percent, which lines up with sets of roughly eight to twelve. Below that you are into speed work, technique practice and warm-ups.

Two cautions on the rep column. First, those reps come from inverting the same formula that produced your max, so they inherit all of its assumptions and become steadily less believable as the numbers grow — the figure the arithmetic gives for fifty percent is not a set anyone should attempt. Second, the reps listed against a percentage describe what that load theoretically allows, not what you should program. Working to failure on every set is a different decision, and usually a worse one.

Using an estimate you never tested

The most useful thing about an estimated max is that it is cheap enough to recalculate constantly. Log a heavy top set each week, run it through the same formula, and you get a strength curve without ever peaking for a test.

Read the curve rather than any single point. A projection that climbs steadily over eight weeks is telling you something real, even if every individual number is a few percent off, because the error is broadly consistent from week to week. A projection that jumps around usually reflects how close each set was to failure rather than anything about your strength.

When it comes time to attempt a genuine single, treat the estimate as a planning figure rather than a target. Openers are typically set well below it, and there is no cost to an attempt that goes up easily — whereas a missed one costs you the attempt, the energy, and sometimes more.

Where the number stops being useful

An estimate is only as good as the set behind it. If the reps you entered were not genuinely close to failure, the projection lands low; if form broke down on the last one, it lands high, because a rep that was not a clean rep should not have been counted.

The formulas also carry the shape of the people they were fitted to. They were built largely on trained lifters, which tends to make them less reliable for beginners, whose numbers move quickly and whose rep performance at a given percentage is often not typical yet. Lift selection matters too — the relationship between reps and max is not the same for a deadlift as for an overhead press, and none of these formulas knows which lift you did.

Finally, none of this speaks to whether attempting a heavy single is a good idea for you on a given day. That depends on your training history, your recovery, your joints and your technique under load, and it is a conversation for a coach or a qualified professional rather than a calculator.

Frequently asked questions

How do I calculate my one rep max?

Take a set you completed with good form, then apply one of the published equations. With Epley the arithmetic is your weight multiplied by one plus your reps divided by thirty — so 84 kg for 6 reps gives 84 × 1.2, or 100.8 kg. Brzycki and Lombardi use different arithmetic on the same two inputs and will land a few kilos either side.

Which 1RM formula is the most accurate?

None of them is reliably most accurate for everyone, because each was fitted to a different group of lifters. Epley is the most widely used and is the default here. Brzycki usually returns the lower figure, which is the safer one to load a bar with. What matters more is staying with one formula so that changes you see over time reflect your training rather than a change of equation.

Why does the calculator only allow up to ten reps?

Beyond roughly ten reps a set measures endurance as much as strength, so the relationship the formulas rely on becomes unstable. Brzycki is the clearest example: its denominator shrinks as reps rise and the estimate eventually runs away entirely. For a dependable projection, use a set of three to six reps taken close to failure.

What percentage of my one rep max should I train at?

It depends what you are training for. Heavy singles and doubles sit around ninety percent and above, primary strength work in the eighty to ninety band, and the range commonly called the hypertrophy zone around sixty-five to eighty percent, which corresponds to roughly eight to twelve reps. Lighter loads still have a place for speed work and technique.

Is an estimated one rep max the same as a tested one?

No. A tested max is a measurement, an estimate is a projection from a set you already did. The estimate is usually within a few percent for lifters with a bit of experience, but it can be well out if the set was not close to failure or if form slipped on the final rep. Treat it as a planning figure, not as a number to walk up and attempt.

Does one rep max transfer between exercises?

Not usefully. A max is specific to the lift and to your leverages and technique in it. Knowing your squat max tells you very little about your bench, and the two often move at different rates across a training block. Estimate each lift you care about separately.

Why do the three formulas give different answers?

Because each was derived from a different group of lifters and fitted with a different shape of equation. Epley rises in a straight line with reps, Brzycki puts reps in the denominator and reads lower as sets get longer, and Lombardi uses a small power that flattens out at the top end. They agree closely at low reps and separate as the count climbs, which is itself a reasonable measure of how much confidence the projection deserves.

This calculator produces an estimate derived from published equations, not a measurement of your strength, and it is not medical or coaching advice. Maximal lifting carries real injury risk. Warm up thoroughly, use a spotter for any lift where failure could trap you under the bar, and stop if form breaks down. If you have a heart condition, a recent injury, high blood pressure, or any other reason to be cautious under heavy load, speak to a qualified healthcare professional before attempting maximal or near-maximal lifts. Learn more about how we build our calculators and read our privacy policy.