Fitness calculator
One-Rep Max Calculator
Estimate maximum strength without performing a true one-rep test.
Uses the Epley estimate. Best suited to controlled sets of 1–10 repetitions; do not exceed safe loads.
Estimated one-rep max
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How weight and reps turn into an estimate
"Weight lifted" must be greater than zero, and "Repetitions" is restricted to whole numbers from 1 to 30. Entering 1 rep is treated as a special case: the calculator returns your entered weight unchanged, and the "Formula" detail line switches from the equation to simply reading "Weight lifted," because a single rep already is a true one-rep max — there's no estimating left to do.
For any rep count from 2 to 30, the Epley formula runs directly. Above 30 reps, or with reps at zero or blank, the result field goes empty instead of extrapolating a number the formula was never designed to produce.
The Epley formula
Lifting 100 units for 5 reps gives 100 × (1 + 5 ÷ 30) = 100 × 1.1667 ≈ 116.67. A 185 lb lift for 3 reps gives 185 × 1.1 = 203.5 lb, and a 225 lb bench press for 8 reps gives 225 × (1 + 8 ÷ 30) ≈ 225 × 1.2667 = 285.00 lb.
A 140 kg deadlift for 12 reps gives 140 × 1.4 = 196.0 kg — note that 12 reps is inside the calculator's allowed 1–30 range but past the roughly 10-rep point where rep-based formulas are generally considered reliable, so treat a number like this as a rough ballpark rather than a precise max.
Where Epley diverges from a true maximum
Epley assumes the relationship between reps and percentage of your true max is a straight line, but the real strength-endurance relationship curves, and different published formulas disagree more the higher the rep count goes. Take the 225 lb for 8 reps example: the Brzycki formula, weight ÷ (1.0278 − 0.0278 × reps), gives 225 ÷ (1.0278 − 0.2224) = 225 ÷ 0.8054 ≈ 279.36 lb — about 5.64 lb, or 2%, below Epley's 285.00 lb estimate from the identical inputs.
This is a training estimate, not medical advice, and it isn't a substitute for a supervised, properly warmed-up attempt at a true single-rep max. Treat any number from a set of 10 or more reps as directional rather than a figure to load directly onto a bar.
Using an estimated max to plan training
A single 1RM estimate is usually a starting point for setting working weights, not an end in itself:
- 185 lb for 5 reps → estimated 1RM of 185 × (1 + 5 ÷ 30) = 215.8333 lb
- 70% training load from that estimate: 215.8333 × 0.70 = 151.0833 lb
- 85% training load from that same estimate: 215.8333 × 0.85 = 183.4583 lb
- A true single-rep squat test at 315 lb returns exactly 315, since 1-rep entries skip the formula entirely
- 225 lb bench for 8 reps returns 285.00 by Epley versus roughly 279.36 by Brzycki — a reminder to treat any higher-rep estimate as approximate
Frequently asked questions
Why does entering 1 rep just return the weight I typed?
The calculator skips the Epley formula for a single rep and returns your entered weight directly. Running 1 rep through the formula would actually inflate the number by about 3.3% (since 1 + 1 ÷ 30 = 1.0333), but a 1-rep set is already a genuine max attempt, so no estimate is needed.
Why is there no result above 30 reps?
Repetitions are capped at 30 in this calculator because the formula's accuracy falls apart at very high rep counts — a blank result past that point is a deliberate limit, not a bug.
How reliable is Epley compared with other 1RM formulas?
It varies by rep range. For 225 lb at 8 reps, Epley estimates 285.00 lb while the Brzycki formula estimates about 279.36 lb, a roughly 2% gap — and that gap tends to widen further as rep count climbs.
Does the result carry a unit label?
No — the output is a plain number with no kg or lb suffix. It's whatever unit you entered for weight lifted, so keep track of that yourself when reading the result.
Can I use this to plan percentage-based training?
Yes. Once you have an estimate — say 215.8333 from 185 lb for 5 reps — multiply it by a target percentage to get a working weight, such as 215.8333 × 0.70 ≈ 151.08 lb for a 70% set.
Does a higher rep count always lower the estimated max?
No — the opposite. At the same weight, more reps produce a higher estimated max, since weight × (1 + reps ÷ 30) grows as reps increase. The logic is that lifting a given weight for more reps implies you could lift a heavier weight for fewer.
This calculator is for informational and educational purposes only and is not medical advice. Its results are general estimates, not an individual assessment. Talk to a doctor, registered dietitian, or other qualified health professional before making decisions about your health, diet, or exercise.