Knowing your one-rep max is incredibly useful for programming your training — but actually testing it means loading a bar near your limit and grinding out a risky single rep. The good news: you don't have to. You can calculate a reliable estimate from a set you already do in a normal workout. Here's exactly how.
How to calculate your one-rep max
To estimate your one-rep max without a true max attempt, use the Epley formula: 1RM = weight × (1 + reps ÷ 30). For example, 200 pounds for 5 reps estimates a 233-pound max. Apps apply this automatically from any set you log, giving a safe estimate with no max-effort lift required.
That's the whole method in one formula. Take a weight you lifted, the number of reps you got, and plug them in. Let's walk through it so it's crystal clear.
The Epley formula, step by step
The Epley formula is the most widely used 1RM estimator:
1RM = weight × (1 + reps ÷ 30)
To use it:
- Note the weight you lifted (e.g., 200 pounds).
- Count the reps you completed with good form (e.g., 5).
- Divide reps by 30: 5 ÷ 30 = 0.167.
- Add 1: 1 + 0.167 = 1.167.
- Multiply by the weight: 200 × 1.167 = 233 pounds.
So a clean set of 200 pounds for 5 reps estimates a one-rep max of about 233 pounds. No max-out required — just a normal working set.
The Brzycki formula (an alternative)
Epley isn't the only option. The Brzycki formula is another popular estimator:
1RM = weight ÷ (1.0278 − 0.0278 × reps)
For 200 pounds × 5 reps, Brzycki estimates about 225 pounds — close to Epley's 233. Different formulas give slightly different numbers, but they land in the same ballpark. What matters most is picking one and using it consistently so your trend over time is comparable.
How accurate are these estimates?
1RM estimates are most accurate when the rep count is low — ideally between 2 and 6 reps. Here's why: the fewer reps you do, the closer that set is to a true single-rep effort, so there's less extrapolation involved.
- Sets of 2 to 6 reps: very accurate, usually within a few percent of a true max.
- Sets of 7 to 10 reps: still useful, but accuracy drops slightly.
- Sets above 12 reps: estimates become unreliable, because endurance and fatigue tolerance start to dominate over pure strength.
The practical rule: for the best 1RM estimate, use a moderately heavy set in the 3-to-6 rep range. This connects neatly to training in the right rep ranges.
How often should you re-estimate?
Because estimating is safe and effortless, you can do it far more often than you'd ever test a true max. Every time you log a challenging set, you generate a fresh estimate. That gives you a continuous picture of your strength trend rather than occasional snapshots — and a rising estimated 1RM is one of the clearest signs your training is working. (For the bigger picture on what a 1RM is and how to use it, see what is a one-rep max.)
Let the math happen automatically
The formulas are simple, but doing them by hand for every lift, every session, gets old fast — and that's exactly the kind of friction that stops people from tracking. The smarter approach is to let your tracker calculate it for you.
Log one set — get your estimated 1RM automatically with 21 Fitness. Try it free. Speak or log any working set, and the app applies the formula instantly, then charts your estimated one-rep max over time so you can watch your strength climb. From there, you can see how your numbers stack up against strength standards for the bench press.
Frequently asked questions
Which 1RM formula is most accurate? No single formula wins for everyone — Epley and Brzycki are both well-validated and give similar results. Consistency matters more than the specific formula, since you're tracking a trend.
Can I calculate a 1RM for any exercise? The formulas work best for compound barbell lifts like the bench press, squat, and deadlift. They're less reliable for isolation or machine exercises where rep performance varies more.
Internal links: What Is a One-Rep Max? · What Is a Good Bench Press? · How Many Reps to Build Muscle?
External sources: National Strength and Conditioning Association (nsca.com) · National Library of Medicine (pubmed.ncbi.nlm.nih.gov) · American Council on Exercise (acefitness.org)