One-Rep Max (1RM) Calculator

What this 1RM calculator actually does

Testing a true one-rep max on the bar is risky and, honestly, most gyms don't have a spotter free when you want to try it. This calculator estimates your one-rep max (1RM) from a set you already did — just enter the weight and how many reps you got, and it runs the numbers through six different strength formulas (Epley, Brzycki, Lombardi, McGlothin, O'Conner, and Wathan) and averages them out. Averaging six formulas instead of trusting one smooths out the quirks each individual formula has at higher rep counts.

How to use it

• Enter the weight you lifted and how many clean reps you completed.
• If the set wasn't an all-out effort, pick your RPE (how many reps you had left in the tank) instead of leaving it on "to failure" — the estimate adjusts accordingly, the same way a Barbell Medicine-style RPE calculator does.
• Switch between kg and lb depending on how you train.
• Scroll down to the percentage chart to see your working weights for any percentage from 50% to 100% of your max — handy for programming a 5/3/1, Wendler, or linear periodization block.

Why six formulas instead of one?

Every one-rep max formula is a curve fit to lifting data, and every curve fit has a rep range where it's most accurate. Epley tends to run a little high past 10 reps; Brzycki tends to undershoot for very strong lifters at low reps. Averaging six well-established formulas gives you a more stable estimate than betting everything on whichever one a random calculator happened to hardcode.

Real-world use cases

• Programming percentages: Most strength programs (5/3/1, Starting Strength progressions, powerlifting peaking blocks) are written as a percentage of your 1RM. If you don't know your max, you can't hit the right percentages.
• Tracking strength over time: Run the same rep test every few weeks and compare the estimated max instead of grinding out a true single every time, which is fatiguing and adds injury risk.
• Picking a training max: Programs like Wendler 5/3/1 deliberately use 85-90% of your estimated max as a "training max" — this calculator's percentage chart gets you there in one step.

Frequently asked questions

How accurate is a 1RM calculator compared to an actual max attempt?

It's an estimate, not a guarantee — typically within a few percent of your true max when the set you enter is somewhere between 2 and 10 reps. Estimates get less reliable above 12-15 reps, since rep-max formulas are built on lower-rep data.

What's the best rep range to test for an accurate estimate?

3 to 6 reps at a genuinely hard effort gives the most reliable estimate across all six formulas. A 1-rep or 2-rep test is close to your actual max anyway; a 15-20 rep set turns into more of a muscular endurance number than a strength number.

What does RPE mean and why does it change the result?

RPE (Rate of Perceived Exertion) is a 1-10 scale for how close a set was to failure. If you stopped a set at RPE 8, you had about 2 reps left in the tank — so the calculator treats that set as if it were actually closer to failure than the rep count alone suggests, which keeps the max estimate from being artificially low.

Can I use this for any lift, not just bench/squat/deadlift?

Yes — the formulas are generic strength-curve math, not lift-specific, so this works as a max lift calculator for overhead press, rows, or any barbell, dumbbell, or machine exercise where you can do a clean multi-rep set.

Why is my estimated max different from what I actually lifted for a single before?

Skill at low-rep singles (technique, bracing, psych-up) doesn't always match your submax rep strength one-to-one. Treat the estimate as a very solid planning number, not a guarantee of what you'll hit on test day.