What a one rep max is
Your one rep max, or 1RM, is the heaviest weight you can lift once with good technique. Most strength programs, including the 5x5 strength program, prescribe training loads as a percentage of it, so knowing roughly where it sits makes programming much easier.
You do not need to test it to find it. A hard set of a few reps carries enough information to estimate it closely, without the injury risk and fatigue of a true max attempt.
How to use the calculator
Enter the weight you lifted and how many clean reps you managed, from 1 to 12. Use a set taken close to failure, with one rep or less left in the tank, for the best estimate. A comfortable set of 5 with plenty left will underestimate your max.
The calculator shows the estimate from three formulas, their average, and a chart of percentages from 100% down to 50% with the approximate reps you could do at each.
The three formulas
Each formula was derived from a different set of lifters and fits slightly differently across rep ranges.
Epley: 1RM = weight x (1 + reps / 30)
Brzycki: 1RM = weight x 36 / (37 - reps)
Lombardi: 1RM = weight x reps^0.10
Epley and Brzycki agree closely in the 2 to 10 rep range. Lombardi tends to give lower numbers at higher reps. The average smooths out those quirks, which is why it is shown as the headline figure.
Example: 100 kg (220 lb) for 5 reps gives Epley 116.7 kg, Brzycki 112.5 kg and Lombardi 117.5 kg, averaging about 115.6 kg.
Using the percentage chart
| % of 1RM | Approx. reps | Typical use |
|---|---|---|
| 100% | 1 | Max testing, competition |
| 95% | 2 | Heavy singles and doubles |
| 90% | 3-4 | Strength peaking |
| 85% | 5-6 | Strength work, 5x5 style |
| 80% | 7-8 | Strength and size |
| 75% | 9-10 | Hypertrophy |
| 70% | 11-12 | Hypertrophy, technique |
| 65% | 13-15 | Volume work |
| 60% | 16-20 | Warm-ups, speed work |
| 50% | 20+ | Warm-ups, deloads |
Rep numbers are averages. Some people can do more reps at a given percentage, especially on lower body lifts, and everyone gets fewer reps when tired. Our guide to sets and reps for muscle growth explains how to use these zones.
Accuracy and its limits
Estimates are most accurate from sets of 1 to 6 reps and become noticeably less reliable beyond about 10. At high reps, endurance and pain tolerance start to matter as much as strength, and the formulas cannot see that.
Results also vary by lift. Estimates for the deadlift and squat often differ from the bench press for the same rep count. Use the numbers to plan training, not as a substitute for a properly run test if you compete.
Safety
Testing a true one rep max is a skill. If you are new to lifting, have not used a lift for long, or train alone, use this calculator instead of testing.
Never attempt a max bench press without a spotter or safety arms set at the right height. For squats, use a rack with safety pins and learn how to bail out before you need to.
If you do test, warm up gradually, take three to five minutes between heavy attempts, and stop when technique breaks down rather than when the bar stops moving.
Planning training from your 1RM
Once you have an estimate, use it to set working weights rather than guessing each session. A common approach for a strength block is to start at about 75% for sets of 5 and add 2.5% each week until sets feel very hard, then reset slightly higher.
Many lifters now combine percentages with RPE, a 1 to 10 rating of effort where 10 means no reps left. A set of 5 at RPE 8 means you could have done 2 more. If 80% feels like RPE 9 on a bad day, drop the weight a little; if it feels like RPE 6, your max has probably gone up.
Base percentages on a training max of about 90% of your estimated 1RM if you are unsure. It leaves room for bad days and makes it easier to keep adding weight for longer before stalling, which is the approach behind several popular programs.
Re-estimate every four to eight weeks from a hard set of 3 to 5. If the number keeps rising, the program is working. If it stalls for two cycles, look at sleep, food and total volume before changing everything.
Next steps
Track your estimate every few weeks to see whether your program is working, and read progressive overload explained to keep the number climbing. If you compete in powerlifting, the Wilks and DOTS calculator compares your total across body weights, and the plate calculator tells you exactly what to load.
Frequently asked questions
How accurate are one rep max calculators?
From sets of 1 to 6 reps they are usually within a few percent of a true max. Accuracy drops with higher rep sets, especially above about 10 reps.
Which 1RM formula is best?
Epley and Brzycki are the most widely used and agree closely in the low to mid rep range. The average of several formulas is a sensible middle ground.
How often should I test my 1RM?
Most lifters do not need to test true maxes at all. Estimating from a hard set every four to eight weeks is safer and gives similar information.
Should I use reps to failure?
Use a set where you had about one rep left. Grinding to absolute failure adds risk without improving the estimate much.
Can beginners use this calculator?
Yes, and it is safer than testing. Beginners' numbers change quickly, so re-estimate every few weeks.
References
- 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. J Phys Educ Recreat Dance. 1993;64(1):88-90
- LeSuer DA, McCormick JH, Mayhew JL et al. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997;11(4):211-213
Results are estimates for healthy adults and are not medical advice. See our medical disclaimer.
