One-Rep Max (1RM) Calculator

Enter the weight and reps from a hard set. The calculator shows the Epley, Brzycki and Lombardi estimates separately, their average, and the training loads that follow from it.

Runs in your browser; nothing you type is stored or sent. Estimates only, not medical advice. Updated 2 October 2026.

What a one-rep max really tells you

Your one-rep max, or 1RM, is the single heaviest weight you can move for one full repetition of a lift. It matters far beyond bragging rights: nearly every serious strength program prescribes working weights as a percentage of your 1RM. When a program says "5 sets of 3 at 85%," it is speaking the language of your max. Knowing that number — or a good estimate of it — is what lets you load the bar precisely enough to drive progress without grinding into failure every session.

Testing a true 1RM is accurate but costly. It takes a long warm-up, meaningful fatigue, a competent spotter, and a willingness to risk technique breakdown under a maximal load. That is why most lifters estimate their max from a set they have already done. The calculator above does exactly that, using formulas validated in strength research.

How the calculator estimates your max

Feed the tool a submaximal set — say, 185 lb for 5 reps — and it runs three of the most established prediction equations. Epley multiplies your weight by (1 + reps/30). Brzycki divides your weight by a factor that shrinks as reps climb. Lombardi raises the rep count to a small power. Each was fitted to real lifting data, and each has slightly different assumptions, so they rarely agree perfectly.

Instead of hiding that disagreement behind a single confident-looking number, this calculator shows all three side by side and reports their average as the headline estimate. Epley and Brzycki famously return the same answer at exactly ten reps; below ten reps Epley reads a little higher. Seeing the spread is useful — it is an honest picture of the uncertainty baked into any rep-based estimate.

Turning your max into training weights

The real payoff is the percentage table the tool builds for you. Once you have an estimated 1RM, every training load falls out of it: heavy triples live around 90%, classic five-rep strength work sits near 85%, and hypertrophy sets of eight to twelve fall between 67% and 80%. Rather than guessing what to load for tomorrow's session, you read it straight off the table. If you are new to organizing sets and reps this way, our guide to strength programs and progressive overload guide show how to turn these percentages into a week-to-week plan. Once you know the weight you want, our barbell plate calculator tells you which plates to slide onto each side, and warns you when the number cannot be built from the plates your gym actually owns.

Which percentage for which goal

Ranges summarise the American College of Sports Medicine position stand (2009). Later meta-analyses (Schoenfeld 2017; Schoenfeld 2021) show muscle grows across a wide range of loads when sets are taken close to failure, so treat these as defaults, not rules.

How much to trust the number

Rep-based estimates are a starting point, not gospel. Research on 1RM prediction finds the estimate can miss a true max by 10% or more, and the error grows as you use higher rep counts, because fatigue and technique vary more from set to set. The estimate is most trustworthy when it comes from a genuinely hard set of five reps or fewer, which is why the tool caps input at twelve. Interestingly, studies also show that layering in bodyweight, age, height, or body-fat percentage does not sharpen the prediction — the weight-and-reps relationship already carries the useful signal.

Treat your estimated max as a well-informed hypothesis. Use it to program your next few weeks, let your actual performance confirm or adjust it, and when you do test a true single, warm up thoroughly and keep a spotter close. For building the work capacity that makes a bigger max possible, pair this with our hypertrophy training guide.

Common questions

What is a one-rep max (1RM)?

Your one-rep max is the heaviest weight you can lift for a single, full repetition of an exercise. It is the standard reference point for programming strength training, because most training loads are prescribed as a percentage of it — for example, working sets of five at 85% of 1RM.

How accurate are 1RM estimates?

Estimates from a submaximal set are usually reasonable but can vary by 10% or more from your true one-rep max, especially when you use higher rep counts. The estimate is most reliable when it comes from a heavy set of five reps or fewer. It is an excellent starting point for programming, not a guaranteed number — always test true maxes conservatively and with a spotter.

Which formula should I use — Epley, Brzycki, or Lombardi?

There is no single best formula for everyone. Epley and Brzycki are the two most widely used and agree exactly at ten reps; below ten reps Epley returns a slightly higher estimate. Lombardi tends to run higher at low reps. Rather than pick one, this calculator shows all three and an average so you can see the realistic range instead of a single false-precision number.

Why does using more reps make the estimate less accurate?

The formulas are curve fits calibrated for lower rep ranges. As reps climb past about ten, fatigue, technique breakdown, and individual endurance differences grow, so small errors in the input produce large swings in the estimate. That is why this tool caps input at twelve reps and recommends testing with a set of five or fewer.

Does bodyweight, age, or gender change the 1RM estimate?

Research shows that adding anthropometric variables such as gender, age, height, bodyweight, or body-fat percentage does not improve the accuracy of 1RM prediction from reps. The rep-and-weight relationship carries the useful signal, which is why this calculator keeps the inputs simple.

Formula sources

• Epley B. Poundage Chart. Boyd Epley Workout. Body Enterprises, 1985.
• Brzycki M. A Practical Approach to Strength Training. McGraw-Hill, 1998.
• Lombardi VP. Beginning Weight Training. W.C. Brown, 1989.

Calculator results are estimates for healthy adults and are not medical or dietary advice. See the full disclaimer.