One Rep Max Calculator
Estimate your one-rep max (1RM) based on the weight and reps of a recent set.
How this calculator works
This uses the Epley formula, one of the most common methods for estimating one-rep max from submaximal sets — most accurate for rep ranges under about 10.
Estimates become less reliable at very high rep counts.
Using your 1RM for training programming
Once you have an estimated 1RM, many strength programs prescribe training weights as a percentage of it — for example, 70-80% for hypertrophy-focused work, or 85-95% for pure strength work with lower reps.
It's worth re-testing or re-estimating your 1RM periodically (every 4-8 weeks) as strength improves, rather than relying on an outdated number, since training percentages based on a stale 1RM can end up too light to be effective.
A worked example
Lifting 155 lbs for 8 reps: estimated 1RM equals 155 times (1 plus 8/30), or 155 times 1.267, roughly 196 lbs.
For training purposes, 85% of that estimated max would be about 167 lbs, and 70% would be about 137 lbs — common percentage targets for strength-focused versus hypertrophy-focused training blocks respectively.
Using your estimated 1RM for programming
Many strength training programs prescribe work sets as a percentage of 1RM — for example, 5 sets of 5 reps at 80% of your estimated max. Once you have a 1RM estimate, this calculator's percentage breakdowns give you practical starting weights for common rep-range training.
It's worth periodically re-testing or re-estimating your 1RM as you get stronger, since training percentages based on an outdated max will become progressively less accurate (usually too easy) as strength improves.
Frequently asked questions
How accurate is an estimated 1RM?
It's a useful estimate for programming purposes, generally most accurate for sets of 10 reps or fewer, but individual results can vary based on fatigue, technique, and lift type.
Should I actually attempt a true 1-rep max lift?
Estimating from submaximal sets (as this calculator does) is generally safer and sufficiently accurate for programming purposes — true 1RM attempts carry higher injury risk and are typically reserved for competitive lifters or specific testing contexts.
Which formula is most accurate for estimating 1RM?
The Epley formula used here is one of several common options (others include Brzycki and Lombardi) — they generally agree closely for rep ranges under 10, diverging more at higher rep counts.
How often should I re-test my one-rep max?
Many lifters re-test or re-estimate every 4-8 weeks during active strength training, since consistent progress means older estimates become outdated fairly quickly.