One Rep Max Calculator

Last updated November 15, 2026

How to use the one rep max calculator

1. Pick a hard set you did recently. A set of 2 to 10 reps that ended close to failure gives the best estimate.
2. Enter the weight and the reps, then choose lb or kg and the exercise.
3. If you stopped before failure, open More options and add an RPE. An RPE of 8 means you had about two reps left, and the calculator counts those reps too.
4. Select Calculate 1RM.

You get your estimated max, the answer from each of the seven formulas, training weights from 100% down to 50%, and a set of warm-up weights. The calculator uses the Epley formula unless you pick another one under More options.

Rounding is on by default, so training weights land on loads you can build with real plates: the nearest 5 lb or 2.5 kg. You can switch it off under More options. Your lb or kg choice is saved on your device for next time.

What is a one rep max (1RM)?

Your one rep max is the heaviest weight you can lift once, through a full range of motion, with good form. If you can lift it twice, it wasn't your max. It is the standard yardstick for strength in the bench press, squat, deadlift and overhead press, and it is the number most strength programs are built on.

Programs rarely ask you to lift your max. They ask for a percentage of it: five sets of five at 80%, a heavy triple at 90%, speed work at 60%. Without a 1RM, those percentages are guesses.

There are two ways to find it. You can test it by working up to a true single, which is tiring, needs a spotter and carries more risk. Or you can estimate it from a set you have already done, which is what this calculator does. An estimated max is often written e1RM.

1RM formulas explained

Every 1RM formula does the same job. It takes the weight you lifted and the reps you got, and predicts what you could lift once. The seven formulas here were published by different coaches and researchers between 1985 and 1994, each working from their own data, which is why their answers differ. In the equations, w is the weight lifted and r is the number of reps.

Epley (1985)

1RM = w × (1 + r ÷ 30)

The default here and in most lifting apps. It adds about 3.3% to the weight for every rep. It traces back to a poundage chart that strength coach Boyd Epley put together for athletes at the University of Nebraska.

Brzycki (1993)

1RM = w × 36 ÷ (37 − r)

Published by Matt Brzycki. It matches Epley exactly at 10 reps. Below 10 reps it runs a little lower, and above 10 it climbs faster.

Lander (1985)

1RM = 100 × w ÷ (101.3 − 2.67123 × r)

Tracks Brzycki closely across the whole range. The two usually land within about 1% of each other.

Lombardi (1989)

1RM = w × r^0.10

A curve instead of a straight line. It runs high on short sets and low on long ones: at 3 reps it gives one of the highest estimates, and by 12 reps the lowest.

Mayhew et al. (1992)

1RM = 100 × w ÷ (52.2 + 41.9 × e^{−0.055 × r})

Built from bench press data on college men and women. The curve flattens as reps rise, so it handles longer sets more gently than the straight-line formulas.

O'Conner et al. (1989)

1RM = w × (1 + 0.025 × r)

The same shape as Epley with a smaller step of 2.5% per rep. It gives cautious numbers, which some lifters prefer for setting training weights.

Wathan (1994)

1RM = 100 × w ÷ (48.8 + 53.8 × e^{−0.075 × r})

Another curved formula, from the textbook Essentials of Strength Training and Conditioning. You will also see the name spelled Wathen.

Average of all seven

Averaging evens out the quirks of each formula. Pick it from the Formula menu under More options if you would rather not bet on one equation.

Worked example: 225 lb for 10 reps

Say you bench 225 lb for 10 reps. Epley gives 225 × (1 + 10 ÷ 30) = 300 lb. Brzycki gives 225 × 36 ÷ (37 − 10) = 300 lb. The other five formulas land between 281.3 and 303.2 lb, and the average of all seven is 294.8 lb.

In kilos, 100 kg for 5 reps gives 100 × (1 + 5 ÷ 30) = 116.7 kg with Epley.

How accurate is a 1RM calculator?

Accurate enough to plan training with, as long as the set is short and hard. The seven formulas never agree exactly, and the gap between them grows quickly once a set goes past 10 reps. Here is the spread for a 225 lb set.

From 3 to 8 reps the formulas stay within about 18 lb of each other. At 12 reps the gap is 37 lb, and at 15 reps it reaches 73 lb. That is why the calculator warns you above 12 reps.

Research points the same way. Studies that checked these equations against maxes lifters actually tested found them most accurate for sets of fewer than 10 reps. A 1997 study of seven formulas also found that all of them came in low for the deadlift.

A few things move your result:

• How close to failure you went. If you had reps left and don't add an RPE, the estimate will be low.
• How you train. Lifters who practice heavy singles often beat their estimate. Lifters with a lot of endurance often fall short of it.
• The lift. Estimates tend to be closest for the bench press and can run low for the deadlift.
• Your technique. Reps with a shorter range of motion than you'd use for a real max inflate the number.

Treat the result as a range. If two formulas say 295 and 305 lb, your max is about 300.

How to use your 1RM in training

Most programs set the weight for each workout as a percentage of your max. These are typical ranges that coaches use. The numbers in your own program come first.

The percentage table in your results does this math for you. For any other percentage, use the one rep max percentage calculator. For a table you can print and take to the gym, see the one rep max chart.

Some programs, such as 5/3/1, base their percentages on a training max set at 90% of your true max, so that every rep stays crisp. If your program says so, multiply your 1RM by 0.9 first.

How the warm-up sets work

The warm-up table climbs from light to heavy while the reps drop, so you practice the movement without tiring yourself out: about 40% of your max for 8 reps, 55% for 5, 70% for 3, 80% for 2 and 90% for a single. Rest a minute or two after the light sets and three to five minutes before the heavy ones. For barbell lifts, no warm-up weight goes below the empty bar.

How to test a true max safely

You don't need to test a real one rep max to train well. If you want to anyway, stack the odds in your favor.

• Have a few months of steady practice with the lift first. If you are new, use the calculator instead.
• Use a spotter for the bench press, and set the safety bars in a rack for the squat.
• Do the warm-up sets. Never jump straight to a heavy weight.
• Take small jumps near the top, and stop when a rep turns into a grind or your form changes.
• Rest 3 to 5 minutes between heavy attempts and keep it to two or three of them.
• Skip the test when you are hurt, sick or short on sleep.