One-Rep Max Calculator

What this calculator answers

How much you could probably lift once, estimated from one hard set of 1 to 15 reps. It runs seven published one-rep max (1RM) equations side by side, so you see both the average and how far the formulas disagree for your set. It also turns the estimate into training loads at 50–100% of your 1RM, rounded to the plates you have, with the approximate number of reps you could manage at each load.

How to use it

• Weight lifted: the load on the bar for the set, in pounds or kilograms. Changing the unit converts the number already typed, so 165 lb becomes 74.8427 kg.
• Reps: the full repetitions you completed, from 1 to 15. Leave out partial reps and reps a spotter helped with.
• Reps in reserve: how many more reps you could have done. Choose 0 if the set went to failure. The labels also give the matching RPE (rating of perceived exertion), so RPE 8 means 2 reps in reserve.
• Round loads to: the smallest jump your plates allow, for the percentage table. With 2.5 lb plates the smallest jump is 5 lb (one plate each side); with 1.25 kg plates it is 2.5 kg.

Results update as you type. The Try buttons load a single rep, a long set of 12, a metric set and a set stopped at RPE 8. To track progress, press Save for comparison after entering last week’s set, enter this week’s, and save again: the comparison shows the change in the estimate in both pounds and kilograms.

How to calculate your one-rep max from reps

Multiply the weight you lifted by a factor that grows with the number of reps. Two of the seven equations, Epley’s and Brzycki’s, show how:

• $w$ is the weight lifted, in lb or kg. The estimate comes out in the same unit.
• $r$ is the number of reps to failure: the reps you did plus any you had in reserve.

Brzycki’s equation is often printed as $100w \div (102.78 - 2.78r)$, which is the same with rounded coefficients; the two versions differ by about 0.05% or less from 1 to 15 reps. A single rep is already a one-rep max, so the calculator returns the weight itself when $r = 1$, even though Epley’s equation as written gives $w \times 31/30$ there.

1RM formulas compared: Epley, Brzycki, Lombardi and others

These are the seven equations LeSuer et al. tested against real 1RM lifts in 1997. Each estimates the same thing from the same two numbers, but each was fitted to different lifters or charts, so they give different answers.

At 7 reps the factors run from 1.175 (O’Conner et al.) to 1.240 (Wathan), a gap of 6.5% of the weight lifted. At exactly 10 reps Epley and Brzycki agree: both multiply by 4/3, so 165 lb for 10 reps gives 220 lb with either one.

Worked example: 165 lb for 7 reps

A lifter benches 165 lb for 7 reps and could not have done an eighth, so the reps counted are $r = 7$.

1. Epley: 165 × (1 + 7 ÷ 30) = 203.5 lb.
2. Brzycki: 165 × 36 ÷ (37 − 7) = 198 lb.
3. The other five give 199.8 lb (Lander), 200.4 lb (Lombardi), 204.4 lb (Mayhew et al.), 193.9 lb (O’Conner et al.) and 204.6 lb (Wathan).
4. Average: the seven unrounded estimates add up to 1,404.66 lb, and 1,404.66 ÷ 7 = 200.7 lb, which is about 91 kg.
5. Range: 193.9 lb to 204.6 lb. The 165 lb set was 82.2% of the average estimate.
6. Loads: 80% of the unrounded average, 200.67 lb, is 160.5 lb, or 160 lb to the nearest 5 lb, a load Brzycki’s equation puts at about 8 reps to failure.

Which 1RM formula is most accurate?

None is most accurate for everyone. In LeSuer et al.’s comparison, all seven correlated closely with the real 1RMs of 67 untrained college students, yet on the bench press the average error was significantly different from zero for all but two equations, and on the squat for all but one. Several of the equations did not start as studies at all: Richens and Cleather point out that Epley’s comes from a poundage chart and Lander’s began as an estimated chart.

That is why the calculator shows all seven and uses their average as the headline. The average is a middle value, not a proven better one. The useful information is the range: when the formulas agree closely, which formula you pick hardly matters; when they spread apart, treat any single number with caution.

How many reps give the best estimate?

Fewer reps with a heavier weight, up to about 10. Reynolds et al. found that 5-rep maximum tests predicted the 1RM better than 10- or 20-rep tests, and advised using no more than 10 reps in linear equations, because the load you can lift falls off in a curve as reps rise, not in a straight line.

You can see the effect in the table of other rep counts under the result. For the same 165 lb, a set of 4 reps gives estimates from 180 lb to 192.3 lb, while a set of 10 gives 206.3 lb to 222.3 lb. With 135 lb for 12 reps the formulas range from 173.1 lb (Lombardi) to 195 lb (Lander), a spread of 21.9 lb, so the calculator adds a note that the estimate is less reliable. Above 15 reps the equations are not used here at all.

Reps in reserve and RPE: sets that stop short of failure

If you stopped a set with reps left, count them. Helms et al. describe a rating of perceived exertion (RPE) scale based on reps in reserve (RIR), where RPE 10 is a set to failure, RPE 9 leaves 1 rep and RPE 8 leaves 2. They note that 6 reps with none left, 5 with 1 left, 4 with 2 left and 3 with 3 left are roughly the same load, so the calculator adds the reps in reserve to the reps done.

For example, 185 lb for 5 reps at RPE 8 counts as 7 reps to failure and gives an estimated 1RM of 225 lb. Guesses of reps in reserve are more accurate close to failure, and they differ between novice and experienced lifters, which is why the options stop at 3.

1RM percentage chart: weight and reps at each percentage

The percentage table under the result multiplies your estimated 1RM by 100%, 95% and so on down to 50%, and rounds each load to your plate increment. Its reps column is Brzycki’s equation solved for reps, $r = 37 - 36p$ (with $p$ the percentage as a decimal), rounded down. Epley’s equation solved the same way, $r = 30(1/p - 1)$, gives different counts:

Epley’s line reaches 100% at zero reps, which is the same quirk that makes it overshoot for a single. Real lifters vary more than either equation suggests: in Richens and Cleather’s leg press test, endurance runners averaged 39.9 reps at 70% of their 1RM and weightlifters 17.9. Use the reps column as a starting point and adjust to what you actually manage.

Bench press, squat and deadlift: does the formula change?

The equations are the same for every lift, so there is no separate bench press or squat formula here. What changes is how well they fit. In LeSuer et al.’s test, every equation underestimated the deadlift, while only two equations on the bench press and one on the squat had an average error not significantly different from zero. If you estimate a deadlift, your true max may well be higher than the calculator suggests.

Reading the result

• Estimated one-rep max is the average of the seven estimates, with the lowest and highest just below it.
• Epley and Brzycki show the two equations above on their own; the third tile converts the average to the other unit.
• 1RM by formula lists each estimate, how far it sits from the average, and the factor it multiplies your weight by. The average is in the last row.
• Training loads by percentage of your 1RM gives the load at each percentage, rounded to your plate increment (or exact, if you choose Exact), with the reps you might manage there.
• How this was calculated shows every equation with your numbers.
• Estimated 1RM at other rep counts keeps your weight and changes the reps by up to 3 each way, so you can see what one more rep next time would mean, and how the gap between the formulas grows with reps.

Assumptions and limitations

• The set was taken to failure, or the reps in reserve are counted. A set that stopped short without them counted underestimates your max.
• All seven equations were fitted to groups of people, mostly on barbell lifts. Your own max can fall outside their range, especially from sets of more than 10 reps.
• One set, done fresh. The last set of a long workout, when you are tired, can give a lower estimate.
• The average weighs every formula equally, and the reps column uses Brzycki’s equation alone.
• These are population-based estimates for training, not coaching or medical advice.

Common mistakes

• Entering a set that wasn’t to failure as if it were. Five easy reps with 3 more in the tank is an 8-rep effort; choose 3 reps in reserve or the estimate comes out low.
• Using a very long set. A 15-rep burnout set says more about endurance than strength, and the formulas spread widely there.
• Counting help from a spotter or partial reps. Only full reps you completed yourself belong in the count.
• Mixing up pounds and kilograms. A 100 typed with lb selected is 45.4 kg, not 100 kg; check the unit before reading the result.
• Loading the exact percentage. 160.5 lb can’t be loaded with 2.5 lb plates. Choose the increment your plates allow under Round loads to, and the table shows loads you can put on the bar.
• Treating the reps column as a prescription. It is an average relationship; your reps at 70% or 80% may be far from it.