225 lb x 8 reps one rep max

A one rep max (1RM) is the heaviest weight you can lift for a single complete repetition of an exercise. Testing it directly is slow and carries injury risk, so lifters instead estimate it from a lighter, higher-rep set using a regression formula built from the well-documented relationship between load and repetitions to failure. This calculator uses the Epley formula, 1RM = weight × (1 + reps ÷ 30), as its primary estimate because it's simple, widely used in strength programs, and reasonably accurate across common training rep ranges.

As a second reference point, the calculator also shows the Brzycki formula: 1RM = weight × 36 ÷ (37 − reps). Brzycki and Epley agree closely in the 3-6 rep range but diverge more as reps climb — Brzycki tends to project a slightly lower 1RM at higher rep counts, while Epley tends to run a bit higher. Neither formula is more "correct" than the other; showing both gives you a realistic range rather than a single falsely precise number.

Both formulas lose accuracy as reps increase, and that effect becomes pronounced beyond about 10-12 reps. The underlying assumption is that the relationship between load and reps-to-failure is roughly linear (or close to it), which holds reasonably well for low-to-moderate rep sets but breaks down at higher rep counts where muscular endurance, fatigue, and bar speed start to matter more than raw strength. If you enter 15+ reps, treat the output as a rough ballpark rather than a number to load on the bar.

The percentage table below the calculator converts your estimated 1RM into working weights for common training percentages — from 50% for light technique or warm-up work up to 100%, the estimated max itself. Percentage-based programming (using set percentages of 1RM to structure training blocks) is standard in strength and powerlifting programs, and this table saves you from doing that multiplication by hand for every session.

For the most reliable estimate, use a set taken close to muscular failure with good form — a 1RM formula assumes the reps performed represent genuine effort, not a set stopped several reps short. Re-testing periodically (for example, every 4-6 weeks) keeps the estimate current as your strength changes, and it's always a reasonable idea to work up to true 1RM attempts gradually and with a spotter rather than relying solely on a calculated estimate for max-effort work.