Which 1RM formula is the most accurate?

None of them is reliably best across all lifts and all people, which is the honest answer. Brzycki tends to read slightly lower at higher reps and Epley slightly higher, so lifters often pick whichever flatters them. Rather than choose for you, this tool shows all six and takes the median, which is resistant to any one formula behaving oddly at your rep count. If you have previously tested a true 1RM, compare it against these estimates and note which formula matched — that one is the best predictor for you specifically.

How many reps should I use for the best estimate?

Three to six. Below three you are close to testing a genuine max anyway, and the calculator adds little. Above ten the formulas diverge sharply and the set starts measuring muscular endurance rather than maximal strength. If you enter more than ten reps a warning appears, because that estimate is a rough guide rather than a number to plan loads from.

Does it work for every exercise?

It works best for compound barbell lifts — squat, bench press, deadlift, overhead press — which is what the underlying research measured. It is less reliable for isolation movements, where technique and stabiliser fatigue dominate, and for the deadlift specifically many lifters find their true max comes in below the prediction because grip and lower back fatigue cut the set short before the prime movers do. Treat isolation estimates as very rough.

Should I use this number to decide my max attempt?

No. The uncertainty band here is around ten percent, which is acceptable when picking a working weight and dangerous when picking an attempt. If a set feels too heavy you rack it; if a single is too heavy you are under a loaded bar. Use the estimate to plan percentages between test days, and let the warm-up singles on the day itself tell you what the opener should be.

Why is my estimate different from another calculator's?

Almost certainly because the other one uses a single formula and does not say which. Epley and Brzycki can differ by well over ten percent at higher rep counts, so two sites can both be correct and still show different numbers. This tool lists every formula and its result so you can see exactly where any difference comes from rather than having to guess.

Is my data saved anywhere?

No. The calculation happens entirely in your browser, nothing is uploaded, and the tool works with the network disconnected. Your training numbers never leave the device.

🏋️ 1RM Calculator — Estimate Your One Rep Max

Enter the weight you lifted and how many reps you got, and you get an estimated one-rep max from six different published formulas at once, with the median highlighted as the working figure. Below that is a table showing what to load for one to fifteen reps, which is the part most people actually use week to week. Everything runs in the browser and nothing is stored or sent anywhere.

A one-rep max, or 1RM, is the heaviest weight you could lift for a single repetition of an exercise. A 1RM calculator estimates that number from a set you have already completed, so you can plan training percentages without attempting a true maximal lift.

Weight lifted

Reps completed

Reading this honestly

These are estimates from published regression formulas, not a measurement. They were derived from group averages, so an individual can sit well outside them — fast-twitch-dominant lifters usually test higher than predicted, endurance-trained lifters lower. Accuracy is best from sets of 3 to 6 reps and degrades quickly above 10. The formulas also assume the set was taken close to failure with clean technique; a set left three reps in reserve will under-predict, and a grinding rep with form breakdown will over-predict. Use the number to plan percentages, not to decide what to attempt on a one-rep day.

Private by design. This tool runs entirely in your browser — nothing you enter is uploaded or stored, and it works offline.

About

There is no single correct 1RM formula, which is why this tool shows six rather than picking one and pretending. Epley, Brzycki, Lander, Lombardi, O'Conner and Wathen were each derived from different populations performing different lifts, and they disagree — mildly at low reps, substantially at high ones. At three reps they typically land within two or three percent of each other. At twelve reps the spread can exceed ten percent, which is a different weight on the bar entirely. Showing the range makes that uncertainty visible instead of hiding it behind one confident-looking number, and the median is used as the headline because it ignores whichever formula is behaving as an outlier for your particular rep count.

The practical consequence is that the fewer reps you enter, the more you should trust the result. A set of three to six is the sweet spot: heavy enough that the formulas were calibrated there, light enough that you are not effectively testing a max anyway. Above ten reps the estimate becomes a rough guide, because at that point the set is limited as much by local muscular endurance and conditioning as by maximal strength, and those two qualities do not scale together across people. Someone who trains for endurance will hit fifteen reps at a percentage that would stop a powerlifter at eight, and no formula built on group averages can tell which of them you are.

All six formulas assume the set was taken to or very near failure with technique intact. This assumption is where most real-world error comes from. If you stopped with three reps still in reserve, the calculator sees a set that looked easier than your true capacity and will under-predict. If the final rep was a grinding partial with your back rounding, it sees a rep that did not really happen at that quality and will over-predict. Being honest with yourself about how close to failure the set actually was matters more than which formula you prefer.

The training weight table uses the inverse of the Brzycki relationship, where the fraction of your 1RM available for a given number of reps is (37 − reps) ÷ 36. This produces the familiar percentages — roughly ninety-three percent for three reps, eighty-seven for five, eighty for eight — that match how coaching charts have described load for decades. Those percentages are starting points to be adjusted from, not prescriptions. If the weight the table gives you for five reps feels like a comfortable eight, your real 1RM is higher than the estimate, and the correct response is to update the input rather than to trust the arithmetic over your own set.

One thing this number should not be used for is deciding what to attempt on a max-out day. An estimate carrying a ten percent uncertainty band is fine for choosing a working weight and useless for choosing an opener, because the downside of being wrong is a failed lift under a loaded bar rather than a slightly easy set.

How to use

Enter the weight you lifted and switch the unit to kg or lb. The unit is only a label — the arithmetic is identical either way, so the estimate comes back in whatever you entered.
Enter how many reps you completed with that weight. For the most reliable estimate use a set of three to six taken close to failure.
Press Calculate. The median estimate appears first, with the full range across the six formulas underneath so you can see how much they disagree.
Use the training weight table to set loads for your rep ranges — max strength around one to three reps, hypertrophy around six to twelve, endurance above that.
Retest every few weeks from a fresh working set rather than recalculating from the same old number, so the estimate tracks your actual progress.

FAQ

Which 1RM formula is the most accurate?: None of them is reliably best across all lifts and all people, which is the honest answer. Brzycki tends to read slightly lower at higher reps and Epley slightly higher, so lifters often pick whichever flatters them. Rather than choose for you, this tool shows all six and takes the median, which is resistant to any one formula behaving oddly at your rep count. If you have previously tested a true 1RM, compare it against these estimates and note which formula matched — that one is the best predictor for you specifically.
How many reps should I use for the best estimate?: Three to six. Below three you are close to testing a genuine max anyway, and the calculator adds little. Above ten the formulas diverge sharply and the set starts measuring muscular endurance rather than maximal strength. If you enter more than ten reps a warning appears, because that estimate is a rough guide rather than a number to plan loads from.
Does it work for every exercise?: It works best for compound barbell lifts — squat, bench press, deadlift, overhead press — which is what the underlying research measured. It is less reliable for isolation movements, where technique and stabiliser fatigue dominate, and for the deadlift specifically many lifters find their true max comes in below the prediction because grip and lower back fatigue cut the set short before the prime movers do. Treat isolation estimates as very rough.
Should I use this number to decide my max attempt?: No. The uncertainty band here is around ten percent, which is acceptable when picking a working weight and dangerous when picking an attempt. If a set feels too heavy you rack it; if a single is too heavy you are under a loaded bar. Use the estimate to plan percentages between test days, and let the warm-up singles on the day itself tell you what the opener should be.
Why is my estimate different from another calculator's?: Almost certainly because the other one uses a single formula and does not say which. Epley and Brzycki can differ by well over ten percent at higher rep counts, so two sites can both be correct and still show different numbers. This tool lists every formula and its result so you can see exactly where any difference comes from rather than having to guess.
Is my data saved anywhere?: No. The calculation happens entirely in your browser, nothing is uploaded, and the tool works with the network disconnected. Your training numbers never leave the device.