One-Rep Max (1RM) Calculator
Estimates the most you could lift once from a set you actually completed, using the Epley formula. Useful because testing a true maximum is fatiguing and carries injury risk, and because percentage-based programming needs a reference number.
How to use it
- Enter the weight you lifted.
- Enter the number of clean reps completed.
- Read the estimated one-rep max.
The formula and how well it works
Epley estimates 1RM as weight times one plus reps divided by 30. So 225 pounds for 5 reps gives 225 times 1.1667, about 262.5 pounds.
The Brzycki formula is the other common one and takes a slightly different form, giving about 253 for the same input. Below about 10 reps the two agree closely; beyond that they diverge, with Epley producing higher estimates.
Accuracy is good in the 3 to 6 rep range, typically within about 5 percent for a trained lifter. Outside that range it degrades in both directions. A single-rep set is not an estimate at all, and a high-rep set — 15 or 20 reps — is limited by muscular endurance and cardiovascular capacity rather than by maximal strength, so the extrapolation becomes unreliable. Sets of 12 or more can be off by 10 to 15 percent.
The formula also requires the set to be genuinely close to failure. A set of five with three reps left in reserve reflects a much higher true maximum than the calculation suggests, which is the most common reason a calculated 1RM feels wrong.
Why the estimate varies by exercise
The rep-to-maximum relationship is not the same across lifts, and the formula does not know which lift you did.
Exercises with a large range of motion and heavy involvement of large muscle groups — squats and deadlifts — tend to allow fewer reps at a given percentage of maximum, because the systemic and cardiovascular demand accumulates. Estimates from higher-rep sets on these lifts tend to overstate.
Upper-body pressing, particularly bench press, tends to allow more reps at a given percentage, so estimates hold up better across a wider rep range. Isolation exercises for small muscle groups allow more reps still.
Individual variation is substantial and consistent. Some lifters are demonstrably better at single heavy efforts, others at higher-rep sets at submaximal loads — a difference broadly associated with fibre type distribution and neural factors. If your tested maximum consistently comes in above or below the estimate, that offset is real and worth carrying forward as a personal correction.
Using percentages in a programme
The main practical use of a 1RM is prescribing training loads as percentages.
Approximate correspondences:
- 95 to 100 percent for 1 to 2 reps, maximal strength work.
- 90 percent for about 4 reps.
- 85 percent for about 6 reps, a common strength range.
- 80 percent for about 8 reps.
- 75 percent for about 10 reps, typical hypertrophy territory.
- 70 percent for about 12 reps.
- 65 percent for about 15 reps, endurance and technique work.
Testing versus estimating
A true 1RM test is more accurate and costs more. It requires a proper warm-up progression, several near-maximal attempts, competent spotting, and a recovery cost that affects the following days of training. It also carries the highest injury risk of anything in a training week, particularly with a technical breakdown under maximal load.
For most people an estimate from a set of 3 to 5 is sufficient and can be taken from normal training without a dedicated session. Competitive lifters test because the competition itself is a maximal attempt and they need calibration; recreational lifters generally do not need to.
The more useful modern approach is to track estimated 1RM over time rather than treating it as a fixed number. Logging a rolling estimate from your heaviest sets each week gives a trend line, and the trend is what tells you whether the programme is working. A single figure from three months ago is a poor basis for today percentages, which is the usual reason a programme starts feeling either trivially easy or impossible.
Rate of perceived exertion and reps-in-reserve autoregulation sidestep the problem entirely by prescribing effort rather than load, which accommodates the day-to-day variation — sleep, stress, nutrition — that a fixed percentage cannot.
At a glance
| Formula | Epley: weight × (1 + reps ÷ 30) |
|---|---|
| Best accuracy | 3 to 6 reps, within about 5 percent |
| Degrades above | About 10 reps |
| Requires | A set taken close to failure |
Frequently asked questions
How accurate is the estimate?
Within about 5 percent from a set of 3 to 6 reps. Sets of 12 or more can be off by 10 to 15 percent, since endurance rather than maximal strength becomes the limit.
Why does my estimate feel too low?
Usually because the set was not close to failure. A set of five with three reps in reserve reflects a much higher true maximum than the formula assumes.
Does it work the same for squats and bench?
No. Squats and deadlifts allow fewer reps at a given percentage because of systemic demand, so high-rep estimates overstate more on those lifts.
Should I test a true one-rep max?
Only if you compete. Testing costs recovery and carries the highest injury risk in a training week. Tracking an estimated maximum over time is more useful for most lifters.
Read more
Health and fitness math — Every formula here is an estimate with a known error band. Knowing the band is what makes them useful.