One Rep Max Calculator
Estimate the most weight you can lift for a single rep from a set you already performed.
Example
You bench pressed 100 kg for 5 reps.
Epley: 100 x (1 + 5/30) = 116.7 kg
Brzycki: 100 x 36 / (37-5) = 112.5 kg
Average: 114.6 kg
90% of 1RM = 105.0 kg
80% of 1RM = 93.3 kg
So a good single-rep attempt is around 113-117 kg.
How it works
Enter the weight you lifted and the number of reps; we apply Epley (w x (1 + reps/30)) and Brzycki (w x 36 / (37 - reps)) and build a percentage table from the Epley estimate.
Good to know
The One Rep Max Calculator estimates the heaviest weight you could lift for a single repetition of an exercise, based on a set you actually completed at a lighter load. You enter the weight, the number of reps you performed, and your unit (kg or lb), and it returns three numbers: an Epley estimate, a Brzycki estimate, and the average of the two. It is built for lifters who train with barbells or machines and want a target without attempting a risky true max, and for coaches programming loads for a client.
Reach for it when you are setting up percentage-based training, comparing strength over time, or deciding how much to load a working set. Because attempting an actual single-rep max requires a spotter, good technique, and recovery, most people estimate it instead from a recent hard set of a few reps. The calculator also prints a full percentage table (from 100% down to 50% of your estimated max) so you can read off working weights for hypertrophy, strength, or speed work directly.
Read the result as a range, not a fixed number. The two formulas usually disagree by a few percent, so treat the spread between the Epley and Brzycki figures as your realistic ceiling and use the average as a single planning number. Note that the percentage table on this page is built specifically from the Epley estimate, so the percentages will be slightly higher than if they were based on Brzycki or the average.
A practical caveat: feed it a set taken close to failure for it to mean anything. If you stopped a rep or two short, your true max is higher than the estimate; if your last reps had breakdown in form, it may be inflated. Plug in your best recent set per exercise, recheck every few weeks as you get stronger, and always prioritize form and a spotter before chasing a calculated number.
Frequently asked questions
Why do the Epley and Brzycki estimates differ?
They use different equations. Epley scales linearly with reps (w x (1 + reps/30)) while Brzycki uses w x 36 / (37 - reps). At 1 rep Brzycki returns exactly the weight lifted, and the two agree most closely around 10 reps. Using the average smooths out the difference.
How many reps should I use for the most accurate result?
Keep it to a hard set of about 1-10 reps. Both formulas were calibrated for low rep ranges, so accuracy drops as reps climb. Doing 15+ reps tends to overestimate your true one-rep max.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
What is a one-rep max and why does it matter?
A one-rep max (1RM) is the maximum weight you can lift for a single repetition of a given exercise with proper form. It is used as a benchmark for strength and as the basis for percentage-based training programs.
How do I estimate my one-rep max without actually testing it?
You perform a hard set at a submaximal weight for a known number of reps, then apply a prediction formula such as Epley or Brzycki. This calculator does that automatically once you enter the weight and reps.
Which is more accurate, the Epley or Brzycki formula?
Neither is universally more accurate; both are estimates calibrated for low rep ranges. Brzycki tends to give lower numbers at higher reps while Epley scales linearly, and averaging the two is a common way to balance them.
How often should I recalculate my one-rep max?
Many lifters update their estimate every few weeks or whenever a working set feels noticeably easier. Recalculating after a training block keeps percentage-based loads aligned with your current strength.
What percentage of my 1RM should I train at?
It depends on the goal: lower percentages with more reps are often used for muscle size and endurance, while higher percentages with fewer reps are associated with maximal strength. The percentage table here lets you read off loads from 50% to 100% directly.
Does this work for any exercise like squat, bench, and deadlift?
The formulas are most reliable for compound barbell lifts such as the squat, bench press, and deadlift. They are less consistent for isolation movements or exercises where small muscle groups fatigue quickly.
Why does the calculator limit reps to a low number?
The Epley and Brzycki equations were derived from low-rep sets, so accuracy declines as reps rise. Sets above roughly 10 to 15 reps tend to overestimate the true single-rep max.
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