One Rep Max Calculator
Estimated 1RM plus a full percentage table.
Estimate your one rep max from a set taken near failure using the Epley, Brzycki and Lombardi formulas, with a percentage-of-1RM training table.
Entered in kilograms.
Estimates assume the set was taken close to failure. Above about 10 reps the result reflects muscular endurance more than strength, and accuracy drops sharply.
Estimated one rep max
115.5 kg
from 5 reps at 100 kg
Training guide: 85-95% for strength, 70-85% for hypertrophy, under 70% for endurance and technique.
How the One Rep Max Calculator works
A one rep max is the heaviest single repetition you can complete with good form. Testing it directly is fatiguing and carries some risk, so most lifters estimate it from a set of moderate reps, accurate up to about eight reps, and increasingly optimistic beyond that.
Also known as: 1RM calculator · max lift calculator · Epley formula calculator
Estimating a maximum without testing one
A one repetition maximum is the heaviest load that can be lifted once with acceptable technique. Testing it directly is fatiguing, carries injury risk, and requires spotting on most lifts.
Estimation formulas use a submaximal set to predict it. Epley, published in 1985, gives weight times one plus repetitions divided by 30. Brzycki gives weight divided by 1.0278 minus 0.0278 times repetitions.
Lombardi, O'Conner and Wathan formulas also exist and give slightly different answers. Across the common range they agree closely, and they diverge as the repetition count rises.
Where the estimates hold and where they fail
Accuracy is best from sets of two to five repetitions and degrades quickly beyond about ten. A set of fifteen predicts a maximum with a wide margin of error in either direction.
The reason is that muscular endurance and maximal strength are partly separate qualities. Someone with a high proportion of slow-twitch fibres will manage more repetitions at a given percentage than the formula assumes, and their estimated maximum will be too high.
Training history matters too. Lifters who habitually train in high repetition ranges are relatively better at them, and their estimates from high-rep sets overstate. The practical rule is to use a set of five or fewer if the number matters.
Differences between lifts
The relationship between repetitions and percentage of maximum is not identical across exercises. Lower body lifts generally allow more repetitions at a given percentage than upper body lifts.
A set of ten at 75% is realistic in a back squat and difficult in a bench press for the same lifter, which means a single formula applied across all lifts will misestimate at least one of them.
Technically demanding lifts complicate it further. Deadlift maximums are limited by technique breakdown as much as by force production, and Olympic lifts by skill under fatigue, which is why repetition-based estimation is not used for them.
Using percentages to programme
Percentage-based programming prescribes loads relative to the maximum, which requires the maximum to be roughly right and to stay roughly right.
The problem is that it drifts. A maximum established in January is wrong by March in a novice, whose strength changes weekly, and percentages calculated from it become progressively too light.
Autoregulation addresses this by prescribing effort rather than load. Repetitions in reserve, stopping a set with a stated number of repetitions left, adjusts automatically for how the lifter feels on the day and does not require a current maximum at all.
Testing safely if you do
A proper maximal attempt needs a thorough warm-up, progressive singles approaching the target, full recovery between attempts, and competent spotting or safety pins on lifts where being pinned is possible.
It also needs an honest technical standard. A maximum achieved with a form breakdown is not a useful number and is where injuries happen.
For most people training for health or general strength, testing a true maximum is unnecessary. A three or five repetition maximum provides everything needed for programming, carries far less risk, and can be repeated more often without disrupting training.
Where to go next
The One Rep Max question rarely arrives on its own. These are the ones that usually come with it:
- Wilks Score Calculator — Compare powerlifting totals across body weights.
- Power-to-Weight Ratio Calculator — Watts per kilogram, and what it means on a climb.
- Protein Intake Calculator — Daily protein target for your body weight and goal.
- BMI Calculator — Body mass index with category and healthy weight range.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How accurate are 1RM estimates?
Within about 5% when the set was genuinely near failure at 8 reps or fewer. Accuracy falls off sharply past 10 reps, where the result depends more on muscular endurance than on strength. The set has to be close to failure, reps left in reserve inflate nothing, they just deflate the estimate.
Which 1RM formula is best?
Epley and Brzycki agree closely at low rep counts and diverge above 10. Brzycki tends to read lower at high reps, Epley higher. Since neither is definitive, using the average of several is a sensible default.
How should I use percentage of 1RM?
Broadly: 85-95% for strength in the 1-5 rep range, 70-85% for hypertrophy at 6-12 reps, and under 70% for endurance and technique work. Your true daily maximum fluctuates with sleep, stress and nutrition, so treat percentages as guides rather than prescriptions.
Is it safe to test a true 1RM?
For an experienced lifter with sound technique, a spotter and a proper warm-up, yes. For beginners it is generally unnecessary, technique is still changing week to week, and an estimate from a 5RM gives you everything you need to program.
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