One Rep Max Calculator
The short answer: Your one-rep max is the heaviest weight you can lift for a single repetition with good form. This calculator estimates it without a true max test: enter the weight you lifted and the reps you completed, and the Epley formula (weight x (1 + reps / 30)) returns your estimated 1RM plus a table of training loads.
What Is a One-Rep Max?
A one-rep max, written 1RM, is the maximum weight you can lift for one complete repetition of an exercise with proper form. It is the standard benchmark of maximal strength in powerlifting, weightlifting and general strength training. Coaches use it to set training loads: instead of guessing, a program might call for 5 sets of 5 reps at 80 percent of your 1RM, which turns a vague workout into a precise plan.
Testing a true 1RM means working up to a single all-out lift, which carries real risk without a spotter or on technical lifts like the squat and bench press. An estimated 1RM from a submaximal set gives nearly the same programming information with far less risk.
How the Epley Formula Works
This calculator uses the Epley formula, published by Boyd Epley in 1985 and still the most widely used 1RM equation in gyms:
Estimated 1RM = weight lifted x (1 + reps / 30)
The logic is simple. Each additional rep you can perform at a given weight suggests your true maximum is a little higher than that weight, roughly 3.3 percent higher per rep. If you bench 185 pounds for 6 reps, the formula gives 185 x (1 + 6/30) = 185 x 1.2 = 222 pounds as your estimated max. The same relationship works in reverse: divide an estimated 1RM by (1 + reps/30) to find the weight you should handle for a given rep target.
Epley is among the most accurate formulas for sets of 10 or fewer reps, usually within about 5 percent of a true max. It overestimates high-rep sets, which is why this calculator caps inputs at 12 reps and flags sets above 10 as less reliable.
How to Use This Calculator
- Pick a recent heavy set. Use a set taken close to failure, ideally between 1 and 10 reps, on a compound lift such as squat, bench press, deadlift or overhead press.
- Enter the weight. Type the total weight on the bar, including the bar itself. Select pounds or kilograms to match your plates.
- Enter your reps. Type the number of clean reps you completed. Partial or sloppy reps will inflate the estimate, so be honest.
- Read your estimated 1RM. The big number is your estimated max. Use it to set training percentages for your program.
- Use the percentage table. The table shows the weight that corresponds to 2, 3, 4, 5, 6, 8 and 10 reps at your strength level, so you can pick loads for any rep scheme without more math.
Example Calculations
Here are three worked examples showing how the estimate and a common training load (85 percent of 1RM) are derived:
| Weight lifted | Reps | Estimated 1RM | 85% training load |
|---|---|---|---|
| 225 lb | 5 | 262.5 lb | 223.1 lb |
| 135 lb | 8 | 171.0 lb | 145.4 lb |
| 100 kg | 3 | 110.0 kg | 93.5 kg |
Check the math on the first row: 225 x (1 + 5/30) = 225 x 1.1667 = 262.5, and 262.5 x 0.85 = 223.1. The second row: 135 x (1 + 8/30) = 135 x 1.2667 = 171.0, and 171.0 x 0.85 = 145.4. The third: 100 x 1.1 = 110.0, and 110.0 x 0.85 = 93.5.
How Accurate Is the Estimate?
For sets of 1 to 10 reps taken near failure, Epley estimates are typically within 5 percent of a true tested 1RM, which is close enough for programming training loads. Accuracy drops as reps climb past 10 because muscular endurance starts to distort the relationship between reps and maximal strength. A 20-rep set of squats says more about your conditioning than your max.
The estimate also assumes standard barbell lifts. It is less reliable for machines, which remove stabilizer demand, and for lifts where technique breaks down early, like the deadlift for some lifters. Retest every 8 to 12 weeks as you get stronger, and pair strength work with conditioning: a target heart rate calculator keeps your cardio days in the right zone, and a running pace calculator can structure your running workouts. Recovery matters too, so use a daily water intake calculator to stay hydrated and a body fat percentage calculator to track composition changes as your lifts climb.
Frequently Asked Questions
What is a good one-rep max for a beginner?
It depends on body weight, sex and the lift, but common milestones after a year or two of training are benching body weight, squatting 1.5x body weight and deadlifting 2x body weight. Compare against your own past numbers first.
Is the Epley formula accurate?
Yes, for its intended use. Studies rank Epley among the most accurate formulas for sets of up to 10 reps, usually within about 5 percent of a true max. No formula replaces an actual test, but for programming loads it is close enough.
Can I use this calculator for any exercise?
It works best for compound barbell lifts: squat, bench press, deadlift, overhead press and rows. It is less reliable for isolation exercises, machines and bodyweight movements, where the rep-to-max relationship behaves differently.
How often should I test my 1RM?
Most lifters retest or re-estimate every 8 to 12 weeks, often at the end of a training block. More frequent max attempts interrupt training and raise injury risk. Between tests, this calculator keeps your percentages current from ordinary working sets.
Is it safe to attempt a true one-rep max?
It can be, with preparation: a thorough warm-up, conservative jumps, safety bars or a competent spotter, and never attempt one fatigued or injured. But it is never required. An estimated 1RM programs your training just as well for most goals.
What do the percentages in the results table mean?
Each row shows the weight that should correspond to that rep count at your strength level, as a share of your estimated max. For example, with a 262.5 lb 1RM the table shows about 246 lb for 2 reps, which is 93.8 percent of your max. Use these as starting loads for different rep schemes.
Learn More
These calculators cover the rest of your training plan, from conditioning to nutrition: