How to Calculate One Rep Max
To calculate your one rep max, lift a weight for a few hard reps, then put the weight and reps into a 1RM formula. The simplest is Epley: 1RM = weight × (1 + reps ÷ 30). Here is every common formula, worked out by hand.
Want the answer without the maths? Use our free one rep max calculator. It runs all seven formulas below and averages them.
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How to calculate one rep max, step by step
Calculating 1 rep max takes one hard set and a little arithmetic. A one rep max calculation (or 1RM calculation) always follows the same five steps:
- Warm up with a few lighter sets.
- Do one hard set of 2 to 10 reps with good form. Stop when you are close to failure. Sets of 3 to 6 give the most reliable numbers.
- Write down the weight and reps, counting only full reps.
- Put them into a formula from the list below.
- Round the answer to a weight you can load, and use it to plan training.
In every formula below, w is the weight you lifted and r is the number of reps. We use two examples throughout: 100 kg × 5 reps and 225 lb × 8 reps.
Learning how to calculate one rep max by hand helps you check any calculator and understand where the numbers come from. Pick one 1RM formula below and follow the example, or compare a few.
Epley formula
1RM = w × (1 + r ÷ 30)
100 kg × 5: 5 ÷ 30 = 0.1667. Then 1 + 0.1667 = 1.1667. Then 100 × 1.1667 = 116.7 kg.
225 lb × 8: 8 ÷ 30 = 0.2667. Then 225 × 1.2667 = 285 lb.
Epley is one of the most widely used 1RM equations and the easiest to do in your head. It adds about 3.3% for every rep.
Brzycki formula
1RM = w × 36 ÷ (37 − r)
100 kg × 5: 37 − 5 = 32. Then 36 ÷ 32 = 1.125. Then 100 × 1.125 = 112.5 kg.
225 lb × 8: 37 − 8 = 29. Then 36 ÷ 29 = 1.2414. Then 225 × 1.2414 = 279.3 lb.
Brzycki gives lower numbers than Epley at moderate reps. It stops making sense near 37 reps, which is one reason high-rep estimates are unreliable.
Lander formula
1RM = 100 × w ÷ (101.3 − 2.67123 × r)
100 kg × 5: 2.67123 × 5 = 13.356. Then 101.3 − 13.356 = 87.944. Then 10,000 ÷ 87.944 = 113.7 kg.
225 lb × 8: 2.67123 × 8 = 21.370. Then 101.3 − 21.370 = 79.930. Then 22,500 ÷ 79.930 = 281.5 lb.
The McGlothin formula you may see elsewhere is the same equation as Lander once simplified.
Lombardi formula
1RM = w × r0.10
100 kg × 5: 50.10 = 1.1746. Then 100 × 1.1746 = 117.5 kg.
225 lb × 8: 80.10 = 1.2311. Then 225 × 1.2311 = 277 lb.
You need a calculator with a power (xy) button for this one.
Mayhew et al. formula
1RM = 100 × w ÷ (52.2 + 41.9 × e−0.055 × r)
100 kg × 5: −0.055 × 5 = −0.275, and e−0.275 = 0.7596. Then 41.9 × 0.7596 = 31.83, plus 52.2 = 84.03. Then 10,000 ÷ 84.03 = 119 kg.
225 lb × 8: e−0.44 = 0.6440. Then 41.9 × 0.6440 = 26.98, plus 52.2 = 79.18. Then 22,500 ÷ 79.18 = 284.1 lb.
This formula came from a study of bench press strength in college men and women. “e” is the number 2.71828, found on scientific calculators as ex.
O’Conner et al. formula
1RM = w × (1 + 0.025 × r)
100 kg × 5: 0.025 × 5 = 0.125. Then 100 × 1.125 = 112.5 kg.
225 lb × 8: 0.025 × 8 = 0.2. Then 225 × 1.2 = 270 lb.
O’Conner adds 2.5% per rep, so it gives some of the most conservative estimates.
Wathan formula
1RM = 100 × w ÷ (48.8 + 53.8 × e−0.075 × r)
100 kg × 5: e−0.375 = 0.6873. Then 53.8 × 0.6873 = 36.98, plus 48.8 = 85.78. Then 10,000 ÷ 85.78 = 116.6 kg.
225 lb × 8: e−0.6 = 0.5488. Then 53.8 × 0.5488 = 29.53, plus 48.8 = 78.33. Then 22,500 ÷ 78.33 = 287.3 lb.
1RM formula comparison
Side by side, for both examples:
| Formula | Estimated 1RM | vs average |
|---|---|---|
| Epley | 116.7 kg | +1.2 kg |
| Brzycki | 112.5 kg | −3 kg |
| Lander | 113.7 kg | −1.8 kg |
| Lombardi | 117.5 kg | +2 kg |
| Mayhew et al. | 119 kg | +3.5 kg |
| O’Conner et al. | 112.5 kg | −3 kg |
| Wathan | 116.6 kg | +1.1 kg |
| Average | 115.5 kg | – |
| Formula | Estimated 1RM | vs average |
|---|---|---|
| Epley | 285 lb | +4.4 lb |
| Brzycki | 279.3 lb | −1.3 lb |
| Lander | 281.5 lb | +0.9 lb |
| Lombardi | 277 lb | −3.6 lb |
| Mayhew et al. | 284.1 lb | +3.5 lb |
| O’Conner et al. | 270 lb | −10.6 lb |
| Wathan | 287.3 lb | +6.7 lb |
| Average | 280.6 lb | – |
The formulas agree within a few percent at 5 reps, but spread out as reps go up. That is why we average all seven and show the range. When the reps are 1, every formula should give back the weight you lifted, since a single is already your max for that day.
Which formula should you use?
There is no single best one. A study of seven equations found they tracked real maxes closely but each had errors, and all of them underestimated the deadlift (LeSuer and colleagues, 1997). Another found that a 5-rep max predicted the 1RM better than sets of 10 or 20 (Reynolds and colleagues, 2006). The practical answer: use a heavy set, and average a few formulas. Read more in how accurate are 1RM calculators.
Once you know how to calculate one rep max, the rest is simple: use a heavy set, average two or three formulas, and round to a weight you can load.
How do you go the other way, from 1RM to a rep max?
Rearrange the formula. With Epley, the weight for r reps = 1RM ÷ (1 + r ÷ 30). For a 300 lb max, your 5-rep weight is 300 ÷ 1.1667 = about 257 lb. Our engine averages all seven rearranged formulas, which gives about 259.9 lb. The one rep max chart shows this for every rep count.
Frequently asked questions
What is the easiest 1RM formula?
Epley: multiply the weight by (1 + reps ÷ 30). For 200 lb × 6 reps, that is 200 × 1.2 = 240 lb. It is easy to do on a phone calculator.
What is the one rep max equation most people use?
Epley and Brzycki are the two most common. Brzycki is 1RM = weight × 36 ÷ (37 − reps). Many calculators, including ours, average several equations.
Can I calculate 1RM from a set of 12 or 15 reps?
You can, but the result is rough. Formulas spread apart at high reps, and your endurance affects the number more. Use a set of 3 to 6 reps when you can.
How do I figure out my 1 rep max without a calculator?
Use Epley in your head: add about 3.3% per rep. For 100 kg × 5, that is about 100 + 16.7 = 116.7 kg. Round down to a plate you can load.
Sources
- Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
- Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88-90.
- Lander J. Maximum based on reps. National Strength and Conditioning Association Journal. 1985;6(6):60-61.
- Lombardi VP. Beginning Weight Training. Dubuque, IA: W.C. Brown; 1989.
- Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research. 1992;6(4):200-206.
- O’Conner B, Simmons J, O’Shea P. Weight Training Today. St. Paul, MN: West Publishing; 1989.
- Wathan D. Load assignment. In: Baechle TR, ed. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics; 1994:435-446.
- LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research. 1997;11(4):211-213. Abstract
- Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research. 2006;20(3):584-592. PubMed 16937972