You finished a heavy set of five and your training partner asks the obvious question: "What's that for a single?" You could load the bar to a true one-rep max and find out, but most people never need to. A short equation built into a free calculator gives you a number that is accurate to within a few percent, with none of the bar-on-your-chest risk. Two formulas dominate the strength world for a reason, and once you understand what they're doing, you'll never guess your training percentages again.
Use the 1RM Calculator → to estimate your max from any set you've already done.
What a One-Rep Max Actually Tells You
Your one-rep max (1RM) is the heaviest weight you can lift one time with proper technique. It is the single most useful number in resistance training because almost every program prescribes load as a percentage of that max. If your bench 1RM is 225 lb and the program asks for 5 sets of 5 at 75%, you load 170 lb on the bar. Without a 1RM, you are guessing.
But a "true" 1RM is a test, not a workout. It exhausts the central nervous system, takes 30-45 minutes of warming up, and demands a competent spotter. The Department of Defense's Human Performance Resource Center notes that novice lifters in particular should not max out — the injury risk outweighs the information gained. The fix is simple: take a near-maximal set in a safe rep range and use a validated formula to predict the rest of the strength curve.
The Two Most Trusted 1RM Formulas
Dozens of equations have been published since the 1980s, but two have outlasted the rest because they are simple, work for typical lifters, and have been validated against measured maxes in published studies.
The Epley Formula
Boyd Epley, a strength coach at the University of Nebraska and a founder of the National Strength and Conditioning Association, popularized this equation in 1985:
`1RM = weight x (1 + reps / 30)`
Lift 200 lb for 5 reps and Epley estimates your max at `200 x (1 + 5/30) = 233 lb`. The formula assumes a roughly linear relationship between reps and the percentage of your max, which holds best in the 6-10 rep range.
The Brzycki Formula
Matt Brzycki published his equation in 1993, and it uses a steeper curve that becomes increasingly conservative as reps climb:
`1RM = weight / (1.0278 - 0.0278 x reps)`
The same 200 lb x 5 set gives `200 / (1.0278 - 0.0278 x 5) = 224 lb`. Brzycki tracks measured maxes more closely in the 1-6 rep range — the closer you are to a true single, the more it should be trusted.
A 2021 systematic review in the journal Sports Medicine - Open found 1RM tests themselves are highly reliable (intraclass correlation coefficients above 0.90 for trained lifters), and predictive equations land within 2-10% of measured 1RMs across most lifts. No single formula wins universally, which is why most calculators — including our 1RM tool — show several estimates at once and let you pick the one that matches your rep range.
A Worked Example
Say you back-squatted 275 lb for 6 clean reps. Plug the numbers in:
| Formula | Calculation | Estimated 1RM |
|---|---|---|
| Epley | 275 x (1 + 6/30) | 330 lb |
| Brzycki | 275 / (1.0278 - 0.0278 x 6) | 320 lb |
| Average | (330 + 320) / 2 | 325 lb |
A reasonable working number is 325 lb. From here you can program your next block with confidence: 5x5 hypertrophy work at 75% would be ~245 lb, while heavy triples at 87% would be ~285 lb.
Why You Probably Shouldn't Test a True 1RM
Maxing out has a place — powerlifters compete with it, and trained athletes occasionally need to recalibrate. For everyone else, the risk-reward math is bad. The NSCA's official testing protocol calls for a graded warm-up of 5-10 reps at ~50% of predicted max, then 3-5 reps at ~80%, then a series of singles separated by 1-5 minutes of rest, with the actual 1RM achieved within 3-7 single attempts. That is a 30-45 minute test, requiring a knowledgeable spotter or safety pins set correctly, on a day where the rest of your training will be wasted.
A predicted 1RM is within 2-10% of the truth and costs you nothing extra. If your goal is to program a training block — not win a meet — that is more than accurate enough.
How to Use Your 1RM to Program Training
Once you have a number, the NSCA's published load chart maps reps to percentages so you can prescribe weights for any goal:
| Reps Per Set | % of 1RM | Primary Adaptation |
|---|---|---|
| 1 | 100% | Maximal strength |
| 2 | 95% | Maximal strength |
| 3 | 93% | Strength |
| 5 | 87% | Strength / power |
| 6 | 85% | Strength / hypertrophy |
| 8 | 80% | Hypertrophy |
| 10 | 75% | Hypertrophy |
| 12 | 67% | Hypertrophy / endurance |
| 15+ | <65% | Muscular endurance |
Pick the percentage that matches your goal, multiply by your estimated 1RM, and round to the nearest 5 lb. Recalculate your max every 4-8 weeks, especially during a new program — strength gains compound quickly for newer lifters, and stale percentages will undertrain you.
Common Mistakes That Inflate Your Estimate
Three patterns lead people to brag-worthy 1RM predictions they cannot actually hit on the bar.
Related Reading
If you're tightening up your training and recovery, two more pieces are worth your time. Zone 2 training explains the easy-pace cardio that supports lifting recovery without sapping it, and calories in vs calories out walks through the energy and protein math that turns a strength program into actual muscle.
When you're ready to plug in your numbers, the 1RM Calculator will show you Epley, Brzycki, and the average side by side.
This article is for informational purposes only and is not a substitute for medical or coaching advice. Consult a qualified physician or certified strength coach before beginning a new resistance training program, especially if you have a history of cardiovascular disease, joint injury, or other health conditions.
Frequently Asked Questions
How accurate is a 1RM calculator?
Across the most commonly used equations, predicted 1RMs land within roughly 2-10% of measured maxes for trained lifters, with the best accuracy when the input set is in the 3-10 rep range. Outside that range, error climbs quickly.
Should I use Epley or Brzycki?
For inputs of 6-10 reps, Epley is usually closer. For 1-5 reps, Brzycki tends to track measured maxes better. The two formulas converge at exactly 10 reps, and many lifters simply average them.
How often should I recalculate my 1RM?
Every 4-8 weeks for most trainees, or whenever you finish a training block. New lifters and people returning from a layoff often add strength fast enough that monthly checks are warranted; long-time lifters may go 8-12 weeks between updates.
Can I use a 1RM calculator for any lift?
Use it for free-weight compound lifts where it has been validated: back squat, front squat, bench press, deadlift, overhead press, and barbell row. For machines, isolation work, and odd implements, the predictions are unreliable because the strength curves and stability demands are different.
Is it safe to actually test a 1RM?
For experienced lifters with proper technique, a knowledgeable spotter, and correctly set safety pins, yes — but novices should not test true maxes. The NSCA recommends a structured warm-up of 5-10 reps at ~50% predicted max, 3-5 reps at ~80%, and a series of single attempts with 1-5 minutes of rest until a true 1RM is reached. If any of that sounds out of reach, stick to the calculator.
What if my 1RM estimate goes down?
Don't panic. Day-to-day strength varies with sleep, food, stress, and time of day. A single low estimate is noise; two or three across a couple of weeks is signal. Look at recovery before assuming your training is broken.