🏋️ One-Rep Max Calculator

Estimate your one-rep max (1RM) — the most weight you can lift for a single rep — from any set you've already done. Get results from five proven formulas plus a complete percentage chart to plan your training loads.

Last reviewed: June 2026Built & maintained by RahulMethodology & sourcesEstimates for education only — not medical or coaching advice. Always use a spotter and proper form when testing heavy loads.
Best accuracy at 1–10 reps

How the One-Rep Max Estimate Works

Testing a true one-rep max is risky and tiring, so most lifters estimate it instead. You perform a set to near-failure at a weight you can manage for a handful of reps, and a formula projects what you could lift for a single rep. The fewer reps you use (ideally 1–10), the more accurate the estimate — past about 10–12 reps, fatigue and technique drift make the projection less reliable.

The Five Formulas

Because each formula leans slightly differently, the Average option blends all five for a balanced estimate, which is what most lifters should use.

Using the Percentage Table

Strength programs are written in percentages of your 1RM — for example "5×5 at 80%" or "work up to a heavy single at 90%". The training-load table converts your estimated max into real weights for each percentage, with a rough rep guide, so you can load the bar correctly without doing the math mid-workout.

Tips for an Accurate Estimate

Frequently Asked Questions

Very accurate when you enter a set of 1–10 reps taken close to failure — estimates are typically within a few percent of a tested max. Accuracy drops as reps climb past 10–12 because fatigue affects the projection. Averaging several formulas, as this tool does, smooths out the differences.
There's no single "best" formula — Brzycki is excellent at low reps, Epley is the most widely used, and O'Conner is the most conservative. The recommended approach is the Average option, which blends all five for a balanced result.
Most strength programs prescribe loads as a percentage of 1RM (e.g. 5 reps at 80%). The table shows exactly what weight each percentage works out to for your estimated max, so you can load the bar without recalculating each session.
For most people, estimating is safer and just as useful for programming. If you do test a true max, warm up thoroughly, use a spotter or safety bars, and only attempt it occasionally. This calculator lets you track strength without the risk of frequent max attempts.
Yes — the formulas apply to compound barbell lifts like the squat, bench press, deadlift, and overhead press. They're most reliable for these multi-joint movements; isolation exercises can be less predictable.