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One rep max calculator

Estimate your one-rep max from a lifted weight and rep count, with a full training percentage table.

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One rep max calculator
Paste a weight and rep count from a recent set and this tool estimates your one-rep max (1RM) — the heaviest weight you could lift for a single rep — without you having to actually attempt it. It runs the numbers through four well-known prediction formulas, Epley, Brzycki, Lombardi and Mayhew, and reports the average alongside a full training percentage table, so you can plan strength, hypertrophy and endurance work off a single working set.
Enter one set per line as weight;reps, for example 100;5 for a set of five reps at 100 kg. The Formula option picks what feeds the headline number and the percentage table below it: leave it on "Average of all four" to smooth out any one formula's quirks, or pin it to a single named formula if your gym or coach standardizes on one. Units switches every figure between kilograms and pounds, and "Round to nearest 2.5" snaps the estimate and every percentage-table weight to the nearest plate-loadable increment.
The percentage table runs from 50% to 95% of your estimated 1RM in 5% steps, each row paired with a typical rep target and a training zone — strength, hypertrophy or endurance — so you can pick a working weight straight off the list. Paste several sets, one per line, and the tool uses the strongest estimate across all of them; reps above 20 are rejected, since rep-based formulas get unreliable that far from a true max. Windows and Unix line endings both work, and a badly formed line is called out by number rather than silently skipped.
Everything runs in your browser. Your training numbers are never uploaded, so it is safe to use with a private log. Copy the result, download it as a .txt file, or send it to another tool.
FAQ
Which formula should I use?
The default average of Epley, Brzycki, Lombardi and Mayhew is a good general choice, since it smooths out the quirks any single formula has at a given rep range. Pick one formula by name only if you need to match a specific program or coaching standard.
How accurate is a formula-based one-rep max?
It's an estimate, not a measurement — expect it to be within a few percent of a true tested max for sets of 10 reps or fewer, and less reliable the higher the rep count goes. Fatigue, technique and how hard the set was pushed all affect the real number.
What do the percentage table zones mean?
Rows around 85-95% suit low-rep strength work, the 65-84% range suits hypertrophy (muscle-building) rep ranges, and anything under 65% suits higher-rep endurance work. The reps shown for each row are a typical target, not a hard rule.
Can I enter more than one set?
Yes — put one weight;reps entry per line. Each line gets its own estimate, and the percentage table underneath is built from the strongest estimate across all of them.
Is my training data uploaded anywhere?
No. The one-rep max calculator runs entirely in your browser — your weights and reps never leave your device.