How do I calculate my one rep max?

Take a set you completed close to failure and apply one of the standard formulas. The most common is Epley: multiply the weight by one plus the reps divided by thirty. A 100 kg set of five gives 100 × (1 + 5/30) = 116.7 kg. Brzycki is the other formula you will meet most often: weight × 36 ÷ (37 − reps), which puts the same set at 112.5 kg. Neither is more correct than the other, which is the honest answer to a question people expect a single number from.

Which 1RM formula is the most accurate?

None of them, individually, for you. Each was fitted by regression to a particular group of lifters doing particular exercises, so which one is closest depends on your training history, the lift, and how many reps you tested with. On a 100 kg set of five they span 112.5 to 119.0 kg, an average of 115.5. If you want one number, the average of all seven is a more defensible choice than picking a favourite. If you want consistency, pick one formula and never change it — tracking the same estimate over months tells you far more than the absolute value ever will.

Why do the formulas disagree so much on long sets?

Because they are extrapolating far past the data they were built on, and they extrapolate in different shapes — some linear, some exponential, some a power law. At five reps the seven estimates sit within 5.6% of each other. At ten it is 7.4%, at fifteen 21.9%, and at twenty it reaches 45.3%. Brzycki is the clearest illustration of the problem: its denominator is 37 minus your reps, so as reps climb the number runs away, and a 100 kg set of twenty comes out as a 211.8 kg max. The formula is not broken; it is simply being used far outside its range.

How many reps should I use to test?

Three to five, taken close to failure with technique that does not fall apart — though it is worth being precise about why, because the obvious reason is wrong. The seven formulas do not agree most closely at three reps. They are tightest at around five to seven, where they sit within 5.4% of each other, and at three reps the spread is 7.4%, which is exactly the spread you get at ten. The case for a short set is not agreement, it is that a set of three is limited by how much force you can produce, and force production is what a one rep max measures. A long set is limited by fatigue resistance, which is a different quality entirely. Past ten the numbers fall apart regardless: 11.8% spread at twelve, 21.9% at fifteen.

Should I actually attempt a true one rep max?

Rarely, and never casually. A genuine maximal attempt is a skill in itself — the brace, the setup and the willingness to stay under a bar that is moving slowly are all things you get better at with practice, so an untrained max usually understates what you can do anyway. It also carries the most risk of any set you will do, needs a full warm-up, and on a barbell needs either a spotter or the rack pins set. Estimating from a heavy triple gives you almost the same information for a fraction of the cost. This is general information rather than coaching advice.

What percentage of my 1RM should I train at?

It depends what you are training for, and the table on this page turns any percentage into a weight for you. Working from a 116.7 kg max, Epley puts a triple at 106.1 kg, which is 90.9%, a set of five at 100.0 kg or 85.7%, a set of ten at 87.5 kg or 75.0%, and a set of fifteen at 77.8 kg or 66.7%. Broadly, heavier percentages for fewer reps develop maximal strength while lighter percentages for more reps do more for size and work capacity, and most sensible programmes spend time in both.

Why does a single rep skip the formula?

Because one rep at a weight is the one rep max — there is nothing left to estimate. The published formulas do not all respect this. Feed a 100 kg single into Epley and it returns 103.3 kg; feed it into Mayhew and it returns 108.9. Those are artefacts of curves fitted to multi-rep data and then evaluated at the edge of their range, not claims that you can lift more than you just did. This calculator short-circuits a single to the weight you lifted, which is a deliberate departure from the raw formulas and the only sensible answer.

Does this work the same for every lift?

No, and the difference is large enough to matter. Lifts with a big range of motion and a large muscle mass behind them — squats and deadlifts especially — tend to allow more reps at a given percentage than a bench press or an overhead press does, so a rep-based estimate reads differently across the board. Isolation movements are the least reliable of all, because the limiting factor is often local burn rather than force. Use these numbers within a lift, comparing your bench estimate against your own bench history, and not across lifts.

How often should I re-estimate?

Every four to eight weeks is plenty for most people, and there is little point doing it more often than your training actually changes. Strength moves slowly enough that a fortnightly retest mostly measures how you slept, what you ate and how warm you were rather than any real adaptation. Retest the same way each time — same lift, same rep target, same formula — because the comparison is only meaningful if the method holds still. A single estimate is a snapshot; a run of them under identical conditions is the thing worth reading.

One Rep Max Calculator

Your one rep max is the heaviest weight you could lift once, and almost nobody finds it by actually trying. You take a set you have already done — say 100 kg for 5 reps — and run it through a formula. Epley, the most widely used, puts that set at a 116.7 kg max, which makes the set itself 85.7% of y...

YOUR SET

WEIGHT LIFTED (kg)

REPS COMPLETED

REPS

FORMULA

ESTIMATED 1RM

116.7 kg

YOUR SET WAS

85.7 %

Epley · all seven span 112.5–119.0 kg, averaging 115.5

Formula

Epley

Average of seven

115.5 kg

Lowest estimate

112.5 kg

Highest estimate

119.0 kg

Spread

5.6%

In the other unit

257.2 lb

YOUR TRAINING WEIGHTS

REPS

WEIGHT

% OF 1RM

116.7 kg

100.0%

109.4 kg

93.8%

106.1 kg

90.9%

100.0 kg

85.7%

92.1 kg

78.9%

87.5 kg

75.0%

83.3 kg

71.4%

77.8 kg

66.7%

STEPS

You lifted 100.0 kg for 5 reps

Epley applied to 100.0 × 5 reps

The other six formulas give 112.5 to 119.0 kg, a spread of 5.6%

Estimated 1RM: 116.7 kg

SET SIMULATION

An even tempo, which no real set has. The bar here moves at the same speed on every rep. A genuine set close to failure slows down as it goes, and that slowing is the actual signal that the estimate depends on — a set of 5 that still felt fast was not the set this calculator assumes.

HOW THE FORMULAS DIVERGE

All seven estimators applied to 100.0 kg across 1 to 15 reps. Your formula is the solid line and the dashed vertical marks your rep count. They meet at a single rep because a single needs no estimate, sit closest between about five and seven, and fan apart badly beyond ten — which is why a long set makes a poor test.

WHAT EACH FORMULA SAYS ABOUT YOUR SET

Epley

116.7 kg

Brzycki

112.5 kg

Lander

113.7 kg

Lombardi

117.5 kg

Mayhew

119.0 kg

O'Conner

112.5 kg

Wathan

116.6 kg

An estimate, not a number to attempt. These formulas were fitted to groups of lifters, not to you, and they assume the set was taken close to failure with clean technique. Treat the result as a training anchor for choosing percentages — not as a weight to walk up to and try.

Live simulation · drawn to scale · updates as you type

Created with❤️byeaglecalculator.com

HOW TO USE

1
Enter the weight you lifted and the number of reps you completed with it. The estimate assumes that set was taken close to failure — if you stopped with three good reps left, the calculator will understate your max, because the formulas cannot see effort, only numbers.
2
Pick a formula, or leave it on Epley, which is the one most gyms and apps use. The seven bars underneath show what every other estimator makes of the same set, and clicking any bar switches to that formula so you can see the whole table move.
3
Read the training weights table. It is the chosen formula run backwards, so the row matching your rep count returns exactly the weight you entered — a useful check that the two directions agree. Use the percentage column to set your working weights.
4
Look at the divergence chart before trusting a number from a long set. The lines sit close together through the low reps and fan apart badly past ten, which is the clearest argument for testing with a heavy three to five rather than a set of fifteen.

WORKED EXAMPLE

A 100 kg set of 5 reps, taken close to failure, using Epley. Epley is 1RM = w × (1 + r/30), so 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg. That is 257.2 lb. Running it the other way round tells you what the max means in training: the same formula inverted gives 106.1 kg for a triple (90.9% of the max), 100.0 kg for a set of five — which returns exactly the weight we started from, as it must — 87.5 kg for a set of ten (75.0%), and 77.8 kg for fifteen (66.7%). Now the part most calculators leave out. The same set through all seven published formulas: Epley 116.7 · Brzycki 112.5 · Lander 113.7 · Lombardi 117.5 · Mayhew 119.0 · O'Conner 112.5 · Wathan 116.6 The average is 115.5 kg, the range is 112.5 to 119.0, and the spread is 5.6%. That is about as tight as these formulas ever get, because five reps sits in the middle of the data they were built from. Run the same exercise on a set of fifteen and the spread widens to 21.9%; on a set of twenty it reaches 45.3%, with Brzycki claiming a 211.8 kg max from a 100 kg set. Which is the whole argument for testing with three to five.

THE FORMULAS

Epley1RM = w × (1 + r/30)

Brzycki1RM = w × 36 / (37 − r)

Lander1RM = 100w / (101.3 − 2.67123r)

Lombardi1RM = w × r^0.10

Mayhew1RM = 100w / (52.2 + 41.9e^−0.055r)

O'Conner1RM = w × (1 + 0.025r)

Wathan1RM = 100w / (48.8 + 53.8e^−0.075r)

Rep weightw = the same formula, inverted

A single1RM = w, no formula applied

Pounds1 lb = 0.45359237 kg exactly

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Last updated: July 29, 2026 · Formula verified · An estimate fitted to groups of lifters, not a weight to attempt · Not medical or coaching advice · Eagle-eyed accuracy for every calculation.