How this instrument works
Most percentage-based strength programming needs a one-rep max as its reference point, but actually testing a true 1RM takes time, fatigue, and — on lifts like the squat and deadlift especially — real technical risk when pushing a truly maximal attempt. Estimating from a sub-maximal set you've already completed sidesteps that cost: enter the weight and reps, and this calculator projects what a single all-out rep at that same effort level would likely produce.
The formula behind the estimate is Epley's, 1RM = weight x (1 + reps/30), attributed to strength coach Boyd Epley's 1985 poundage chart and one of the two most commonly used one-rep-max estimators across strength sports. It applies the same general logic regardless of which lift you're testing: each additional rep beyond the first represents roughly 1/30th of extra one-rep capacity.
Research backing multi-rep-based 1RM prediction has generally supported the approach: a 2006 study by Reynolds, Gordon and Robergs tested 1, 5, 10 and 20-rep-maximum data against true one-rep performance and found strong predictive relationships, with 5-rep-maximum data producing the tightest accuracy of the rep ranges tested. That pattern — moderate rep counts predicting better than very high ones — holds broadly across lifts, though the precise accuracy shifts somewhat by exercise since fatigue accumulates differently on the squat, deadlift and press than on the bench.
- Enter Weight lifted — the load used for a recent set, on any lift you want to estimate.
- Enter Repetitions completed — how many clean reps you got, ideally close to failure and under about 10 for accuracy.
- Read Estimated one-rep max — the projected single-rep weight the Epley formula calculates.
- Use the estimate to set percentage-based training weights, but re-test periodically as strength changes rather than reusing an old figure indefinitely.
Worked example — 225 for 3 reps
Enter 225 as the weight lifted and 3 as the reps completed. 1RM = 225 x (1 + 3/30) = 225 x 1.10 = 247.5 — an estimated one-rep max of 247.5 from a set well short of an actual maximal attempt.
For comparison, the same formula applied to a much lighter set — 100 lifted for 8 reps — gives 100 x (1 + 8/30) = 126.6667, illustrating how the estimate scales down proportionally with the weight actually lifted, while the added-percentage effect from the rep count stays governed by the same 1/30-per-rep logic either way.
Questions
Does this formula work equally well for any barbell lift?
It applies the same general-purpose calculation regardless of which lift you enter, since it's built on a general observed relationship between reps and relative load rather than a lift-specific model. That said, research on multi-rep-based 1RM prediction has found accuracy varies somewhat by exercise, since fatigue accumulates differently across the squat, deadlift, press and bench as rep count rises — so treat any single estimate as a solid planning number rather than a certified figure.
How many reps should I use for the most reliable estimate?
Lower rep counts, roughly 2 to 6, generally give tighter estimates than very high-rep sets. A 2006 study testing 1, 5, 10 and 20-rep-maximum data against true one-rep performance found 5-rep-maximum testing produced the most accurate predictions among the ranges tested, with accuracy declining as rep count climbed toward 20.
Is this the same calculator as the site's bench-press-specific one-rep-max page?
Same Epley formula, same underlying math — the difference is scope. This page is built for any barbell lift and general strength-training programming. The bench-press calculator applies the identical formula but focuses specifically on that lift, including notes on the particular safety considerations around attempting a true bench-press single without a spotter.
How does this feed into a 5/3/1-style training program?
A 5/3/1-style program's training max is typically 90% of a one-rep max like the one this calculator produces — this site's 531-lifting calculator takes that next step, converting a 1RM into a training max and the working weights for the program's first week. Estimating your 1RM here first gives that calculator a number to start from.
How often should I retest and recalculate my estimated 1RM?
Every few weeks of consistent training is a reasonable cadence, since strength changes gradually with training and recovery rather than overnight. Recalculating from a recent set rather than a much older one keeps any percentage-based programming built on top of the estimate — training max calculations, working-weight targets — aligned with your actual current strength.