How to Calculate One Rep Max: 4 Formulas, Worked Examples, and Training Percentages

If you want to learn how to calculate one rep max, you do not need to load the heaviest bar of your life and hope for the best. You need one hard set, a calculator, and the right formula. A one rep max, or 1RM, is the heaviest weight you can lift for one complete repetition with good form. It is the standard measure of maximal strength, and it is the number that turns vague training into precise programming.

This guide shows you how to calculate one rep max four ways, with full worked examples for a man and a woman, and then turns the answer into training weights you can use in your next session.

Quick Answer: How to Calculate One Rep Max?

Here is how to calculate one rep max in two steps. First, lift a weight you can manage for 3 to 10 clean reps to near failure. Second, plug the weight and reps into the Epley formula: 1RM = weight x (1 + reps / 30).

For example, if you bench press 80 kg for 5 reps, your estimated 1RM is 80 x (1 + 5 / 30) = 80 x 1.1667 = 93.3 kg. If you want to skip the arithmetic, our one rep max calculator does the same math instantly. NASM explains the same method and the safety rules for max testing in its one rep max guide (NASM, One Rep Max Calculator).

What Is a One Rep Max?

A one rep max is the maximum weight you can lift for exactly one repetition of a specific exercise, with proper form. The key word is specific. Your bench press 1RM is not your squat 1RM, and your squat 1RM is not your deadlift 1RM. Every lift has its own number, and you track each one separately.

Lifters who learn how to calculate one rep max use it for three jobs. First, program design: training plans prescribe loads as percentages of 1RM, so a known max turns “lift heavy” into “lift 80 kg for 5 sets of 5.” Second, progress tracking: a rising 1RM is the clearest proof you are getting stronger. Third, comparison: 1RM lets you compare your strength across lifts, body weights, and training blocks on one scale.

There are two ways to find it. You can test it directly by working up to a true single, which is the gold standard but also the riskiest option. Or you can estimate it from a submaximal set with a formula, which is what this guide covers. For 95 percent of training, the estimate is the smarter choice, because it gives you a usable number without the fatigue and injury risk of a maximal single.

Step 1: Pick the Right Test Set

Every formula for how to calculate one rep max starts from the same input: a weight and the reps you completed with it. The quality of that input decides the quality of the estimate, so the test set matters more than the formula.

Follow these rules for the test set. Use a weight you can lift for 3 to 10 reps with good form, taken to near failure, meaning you could maybe do one more rep but not two. Use a compound barbell lift you know well, such as bench press, squat, deadlift, or overhead press. Keep the technique identical to the lift you want the 1RM for. A set with bounced reps, a shortened range of motion, or a spotter pulling the bar does not count.

The rep range matters when you learn how to calculate one rep max, because the formulas were built on low to moderate reps. Sets of 2 to 5 reps give the most reliable estimates. Sets of 6 to 10 reps are still reasonable and much less fatiguing. Above 10 reps, the formulas diverge sharply, and the set starts measuring muscular endurance rather than maximal strength. If your only recent set is 15 reps, do a fresh test set in the 3 to 10 rep window instead of forcing the formula.

How to Calculate One Rep Max With the Epley Formula

The Epley formula is the most widely used way to learn how to calculate one rep max. It was developed by Boyd Epley in 1985, and most calculators and apps default to it.

1RM = weight x (1 + reps / 30)

Worked example: 80 kg for 5 reps. 1RM = 80 x (1 + 5 / 30) = 80 x (1 + 0.1667) = 80 x 1.1667 = 93.3 kg. Each extra rep adds about 3.3 percent to the estimate, which is why the formula stays simple enough to do in your head between sets.

Epley is the best default for most lifters. It works well from about 3 to 10 reps, and it is the formula to use when a program just says “calculate your 1RM” without naming one. Its weakness is that it runs slightly high at higher rep counts, so treat a 12 rep estimate with more caution than a 5 rep estimate.

How to Calculate One Rep Max With the Brzycki Formula

The Brzycki formula is the conservative rival to Epley, and the one many strength coaches prefer when you learn how to calculate one rep max for low rep sets. It was published by Matt Brzycki in 1993.

1RM = weight x (36 / (37 – reps))

Worked example: 80 kg for 5 reps. 1RM = 80 x (36 / (37 – 5)) = 80 x (36 / 32) = 80 x 1.125 = 90.0 kg. Compare that with Epley’s 93.3 kg for the same set. Brzycki reads 3.3 kg lower here, which is typical: below 10 reps, Brzycki runs lower than Epley.

One useful fact about Brzycki: it agrees with Epley exactly at 10 reps. Both formulas return weight x 1.3333 for a 10 rep set. Below 10 reps, Epley reads higher. Above 10 reps, the order flips and Brzycki reads higher. That crossover is why calculators that default to different formulas can disagree on the same set.

How to Calculate One Rep Max With the Lombardi Formula

The Lombardi formula is the odd one out, because it uses an exponent instead of a straight line. That curve shape makes it behave differently across the rep range.

1RM = weight x reps ^ 0.10

Worked example: 80 kg for 5 reps. 1RM = 80 x 5 ^ 0.10 = 80 x 1.1746 = 94.0 kg. Lombardi gives the highest estimate of the four for this set, a touch above Epley. At low reps it runs high, and at high reps it flattens out, which is why some lifters use it as a cross-check rather than a primary formula.

If the exponent looks intimidating, a 1RM calculator handles it. The point of knowing Lombardi when you learn how to calculate one rep max is not to do exponents in your head. It is to understand why a second calculator can return a higher number for the same set without either one being wrong.

How to Calculate One Rep Max With the O’Conner Formula

The O’Conner formula is the simplest linear model of the four, and the most conservative at low reps. It is sometimes called the O’Conner-Coleman formula.

1RM = weight x (1 + reps / 40)

Worked example: 80 kg for 5 reps. 1RM = 80 x (1 + 5 / 40) = 80 x (1 + 0.125) = 80 x 1.125 = 90.0 kg. O’Conner matches Brzycki exactly at 5 reps, though the two formulas take different paths to get there. O’Conner grows more slowly than Epley as reps rise, because it divides by 40 instead of 30, which matters when you learn how to calculate one rep max for higher rep sets, so it is a good choice when you would rather undershoot your training loads than overshoot them.

All Four Formulas Side by Side

Now the comparison that matters when you learn how to calculate one rep max with more than one formula. The same set run through all four formulas gives four different answers, and the spread tells you how much trust to put in any single number.

The same man, bench press, 80 kg for 5 reps:

Formula	Calculation	Estimated 1RM
Epley	80 x (1 + 5 / 30)	93.3 kg
Brzycki	80 x (36 / 32)	90.0 kg
Lombardi	80 x 5 ^ 0.10	94.0 kg
O’Conner	80 x (1 + 5 / 40)	90.0 kg

The spread is 90.0 to 94.0 kg, a 4.0 kg band, and the average is 91.8 kg. At 5 reps the formulas broadly agree, so any of them gives a trustworthy working number. The practical rule is to pick one formula and stick with it. Switching formulas between test days creates fake progress or fake plateaus that are really just math.

The same man, bench press, 70 kg for 10 reps:

Formula	Calculation	Estimated 1RM
Epley	70 x (1 + 10 / 30)	93.3 kg
Brzycki	70 x (36 / 27)	93.3 kg
Lombardi	70 x 10 ^ 0.10	88.1 kg
O’Conner	70 x (1 + 10 / 40)	87.5 kg

The spread widens to 87.5 to 93.3 kg, a 5.8 kg band. Notice that Epley and Brzycki agree exactly at 10 reps, while Lombardi and O’Conner fall about 5 kg lower. This is the pattern to remember about how to calculate one rep max: the higher the reps, the wider the disagreement, which is why the 3 to 10 rep window is the sweet spot.

Which formula should you use? When you learn how to calculate one rep max, use Epley as the default, because it is the most common and the easiest to compare with other lifters. Use Brzycki when you want a conservative number for low rep strength work. Use Lombardi or O’Conner as cross-checks. If your four numbers cluster within a few kilos, the estimate is solid. If they spread widely, your test set was probably too high in reps to trust.

Worked Example: How to Calculate One Rep Max for a Man (Bench Press)

Meet Dan: he bench pressed 80 kg for 5 clean reps, and later 70 kg for 10 reps. We already ran both sets above. His Epley estimate is 93.3 kg from both sets, which is a good consistency check. When two different sets give the same Epley number, the estimate is more believable than either set alone.

His four-formula picture for the 5 rep set is 90.0 to 94.0 kg, averaging 91.8 kg. For programming, Dan should use 93.3 kg (Epley) as his working 1RM, because it is the standard default and his two sets agree on it. His training loads then follow from the percentages table below: 85 percent of 93.3 is 79.3 kg for strength work, and 70 percent is 65.3 kg for hypertrophy work.

One more conversion Dan will use often: his 5 rep max is about 87 percent of his 1RM. So to go the other way, 1RM = 5 rep weight / 0.87. Check: 80 / 0.87 = 92.0 kg, close to the Epley figure of 93.3 kg. That quick 87 percent rule is the fastest way to turn a 5 rep max into a 1RM without a calculator.

Worked Example: How to Calculate One Rep Max for a Woman (Squat)

Now the full picture for a woman, so you can see how to calculate one rep max for squat with the same method. Meet Sara: she squatted 60 kg for 5 reps, and later 55 kg for 8 reps.

Sara’s squat, 60 kg for 5 reps:

Formula	Calculation	Estimated 1RM
Epley	60 x (1 + 5 / 30)	70.0 kg
Brzycki	60 x (36 / 32)	67.5 kg
Lombardi	60 x 5 ^ 0.10	70.5 kg
O’Conner	60 x (1 + 5 / 40)	67.5 kg

The spread is 67.5 to 70.5 kg, a 3.0 kg band, averaging 68.9 kg. Her Epley working 1RM is 70.0 kg.

Sara’s squat, 55 kg for 8 reps:

Formula	Calculation	Estimated 1RM
Epley	55 x (1 + 8 / 30)	69.7 kg
Brzycki	55 x (36 / 29)	68.3 kg
Lombardi	55 x 8 ^ 0.10	67.7 kg
O’Conner	55 x (1 + 8 / 40)	66.0 kg

The spread is 66.0 to 69.7 kg, a 3.7 kg band. Her two sets agree closely: Epley gives 70.0 kg from the 5 rep set and 69.7 kg from the 8 rep set. That agreement is the real signal that you know how to calculate one rep max reliably. When two different sets land within half a kilo of each other, the estimate is trustworthy, and Sara can program from 70.0 kg with confidence.

Rep to 1RM Conversion Chart

This chart answers the reverse question: if your 1RM is known, what weight can you lift for a given number of reps? It is based on the Brzycki relationship, rounded to whole percentages, and it is the quickest way to pick a working weight without running a formula.

Reps	Percent of 1RM
1	100 percent
2	97 percent
3	94 percent
4	92 percent
5	89 percent
6	86 percent
7	83 percent
8	81 percent
9	78 percent
10	75 percent
11	72 percent
12	69 percent

Read it two ways when you use it to learn how to calculate one rep max in reverse. If your 1RM is 100 kg, a 5 rep set should be about 89 kg. If you lifted 89 kg for 5 reps, your 1RM is about 100 kg. Note that Epley gives nearly identical values in the 3 to 10 rep range, so the chart works whichever of the two main formulas you use. Beyond 12 reps, the percentages flatten out and the chart stops being useful, because endurance, not strength, limits the set.

What Percentage of 1RM Should You Train At?

Knowing how to calculate one rep max is only useful if it sets your working weights. Each training goal lives in its own percentage band, and the table below converts the bands into real loads for Dan and Sara.

Goal	Percent of 1RM	Rep range	Dan (bench 93.3 kg)	Sara (squat 70.0 kg)
Maximal strength	85 to 100 percent	1 to 6 reps	79.3 to 93.3 kg	59.5 to 70.0 kg
Hypertrophy (muscle growth)	65 to 85 percent	6 to 12 reps	60.6 to 79.3 kg	45.5 to 59.5 kg
Muscular endurance	50 to 65 percent	12 or more reps	46.7 to 60.6 kg	35.0 to 45.5 kg
Power (explosive lifts)	30 to 70 percent, moved fast	1 to 5 reps	28.0 to 65.3 kg	21.0 to 49.0 kg

Check one row: Dan’s strength band starts at 93.3 x 0.85 = 79.3 kg. Sara’s hypertrophy band tops out at 70.0 x 0.85 = 59.5 kg. Most lifters spend most of their training in the hypertrophy band, visit the strength band for heavy blocks, and use the endurance band for deloads and conditioning. Power work uses lighter loads moved as fast as possible, which is a different skill from grinding heavy reps.

What Percentage of 1RM Should I Train At?

Train at 85 to 100 percent of 1RM for maximal strength, at 65 to 85 percent for hypertrophy, and at 50 to 65 percent for muscular endurance. For power work, use 30 to 70 percent moved explosively. For example, with a 93.3 kg bench 1RM, strength work starts at about 79.3 kg, hypertrophy work runs 60.6 to 79.3 kg, and endurance work runs 46.7 to 60.6 kg. Most training time belongs in the hypertrophy band, with heavy strength blocks layered on top.

Does 1RM Change by Lift?

Yes, and when you learn how to calculate one rep max per lift, the difference is bigger than most lifters expect. The same person has a different 1RM for every lift, because each lift uses different muscles, leverages, and ranges of motion. Your squat 1RM will usually be well above your bench press 1RM, and your deadlift 1RM will usually top both.

The NSCA even publishes lift-specific coefficients that make this concrete. For a 5 rep set, the coefficient is 1.20 for squat, 1.164 for deadlift, and 1.15 for bench press. So the same 100 kg lifted for 5 reps predicts a 120 kg squat max, a 116.4 kg deadlift max, and a 115 kg bench max. The formulas in this guide use one curve for all lifts, which is fine for programming, but the NSCA numbers are a useful reminder that a 1RM belongs to one lift, not to your whole body.

Two more lift-specific notes. The deadlift often reads lower than the formulas predict, because grip and lower back fatigue cut the set short before the prime movers are truly done. Isolation lifts like curls and leg extensions are the least reliable of all, because technique and stabilizer fatigue dominate the set. Use the formulas for compound barbell lifts first, and treat isolation estimates as rough guides.

How to Test a True 1RM Safely

Formulas are estimates. If you ever want to know how to calculate one rep max by direct testing, do it with a plan, not on a dare. Direct testing is only for lifters with at least 6 months of solid training and reliable technique. Beginners should not attempt a true max, because technique breaks down first at heavy loads, and that is where injuries happen.

If you are ready to test how to calculate one rep max directly, follow this protocol. Warm up with a light weight for 6 to 10 reps at about 50 percent of your predicted max, then 5 reps at 60 percent, 3 reps at 70 percent, 2 reps at 80 percent, and 1 rep at 90 percent, resting 2 to 5 minutes between sets. Then attempt your predicted max for one rep. If it moves cleanly, add 2.5 to 5 kg and try once more after a full rest. Limit yourself to three to five heavy attempts in total, and stop the moment form breaks down.

Spotter rules are non-negotiable. Never test a true 1RM alone. For bench press, use a spotter behind the bench who knows how to take the bar, or use a power rack with safety pins set just below chest level. For squat, use a rack with safeties or two side spotters, and practice bailing with a light weight first. For deadlift, use a platform and be ready to drop the bar. Stop at once if you feel pain, dizziness, or a form breakdown you cannot correct. A missed lift is data, not failure.

How to Retest and Progress

A 1RM is a snapshot, not a permanent number, so knowing how to calculate one rep max once is not enough. Retest or recalculate every 4 to 8 weeks, or whenever you finish a training block. The cleanest method is to repeat the same test: same lift, same formula, same rep range, same conditions. If your 5 rep bench goes from 80 kg to 82.5 kg, your Epley estimate rises from 93.3 kg to 96.3 kg, and your working weights move up with it.

Between tests, use your current 1RM to set loads, and add weight when the top sets start feeling easy. If your 1RM is not moving after two blocks, look at the usual suspects before blaming the formula: sleep, total calories, protein intake, and program volume. Strength follows recovery as much as it follows effort. To check the food side, our guide to how many calories a day shows how to size your intake, and our guide to how to calculate macros shows how to split those calories into protein, carbs, and fat. Your resting burn comes from our guide to how to calculate BMR. If fat loss is the goal and the scale is stuck, our guide to why am i not losing weight covers the other reasons a stall happens.

One more tracking tip: record your 1RM relative to body composition, not just body weight. Two lifters at 80 kg can have very different strength potential if one carries more muscle. Our guide to how to calculate lean body mass and our guide to how to calculate body fat show how to measure what your weight is made of, which puts the 1RM in context.

How Often Should I Recalculate My One Rep Max?

Recalculate your 1RM every 4 to 8 weeks, or whenever you finish a training block. Your max shifts as you get stronger, and stale numbers lead to working weights that are too light. Use the same formula and the same rep range each time, so changes in the estimate reflect real strength changes rather than formula changes. If you switch formulas, note the switch in your log.

How Accurate Is a Calculated 1RM?

A calculated 1RM is an estimate, and honest lifters treat it that way when they learn how to calculate one rep max. Based on sets of 3 to 5 reps with good form, expect the estimate to land within about 5 to 10 percent of your true max. That band is narrow enough to pick working weights, and too wide to pick a competition attempt. Never use an estimate to decide an opener at a meet. Let the warm-up singles on the day tell you what the opener should be.

Accuracy falls off in three situations. Above 10 reps, the formulas diverge and endurance limits the set. On isolation lifts, technique and stabilizer fatigue dominate. And for beginners, the estimate can read high or low because technique is still changing week to week. Day-to-day variation also matters: sleep, food, and accumulated fatigue can move your true max by a few kilos on any given day. That is normal, and it is why programs use percentages and rep targets rather than chasing an exact number.

The best accuracy habit when you learn how to calculate one rep max is consistency. Use the same formula, the same lift, the same rep range, and the same conditions every time you estimate. A consistent estimate that you can compare month to month beats a theoretically perfect formula that you keep changing.

Why Do Different Calculators Give Different 1RM Numbers?

Different calculators give different numbers because they default to different formulas. One calculator may use Epley while another uses Brzycki, and for an 80 kg x 5 set those two return 93.3 kg and 90.0 kg. Some calculators also average several formulas, which lands between the extremes. None of them is wrong. If you want to compare numbers across calculators, check which formula each one uses, or run your set through all four formulas yourself.

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