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Updated October 9, 2026
One Rep Max Calculator
Estimate your one-rep max without maxing out. Enter the weight you lifted and how many reps you did, and get your estimated 1RM plus the percentages coaches use to program training.
What this calculator does
This one rep max calculator estimates the heaviest weight you could lift for a single repetition, using the weight and reps from a recent submaximal set. It then converts the estimate into the training percentages (95 down to 70 percent) that strength programs use to set working weights. No need to attempt a true max, which carries the highest injury risk.
How the math works
It uses the Epley formula (1985), the most widely used 1RM estimate:
- 1RM = weight × (1 + reps ÷ 30)
- Training load = 1RM × percentage (for example, 80% = 1RM × 0.80).
Worked example
You bench 100 kg for 5 reps. Estimated 1RM = 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = about 117 kg. Your 80% training weight is 117 × 0.80 = about 93 kg, and 90% is about 105 kg.
How to use the percentages
Strength programs typically work at 85 to 95 percent of 1RM for heavy strength (1 to 5 reps), 70 to 85 percent for hypertrophy (6 to 12 reps), and below 70 percent for technique and volume work. Because any estimate has error, round down rather than up when the number sits between plates.
Limitations
The Epley formula is an estimate, usually within about 5 to 10 percent for sets of 10 reps or fewer, and it drifts further off beyond that. Estimates also vary by lift: they tend to run high for squats and low for isolation moves. Beginners should not test true maxes; use conservative estimates and a spotter. This is general fitness information, not medical advice.
Planning estimate only. Results use the list prices shown and may differ from your actual bill. Terms
Frequently asked questions
What is a one-rep max?
Your one-rep max (1RM) is the heaviest weight you can lift for one full repetition with good form. It is the standard measure of maximal strength and the reference point coaches use to set training loads as percentages.
What is the Epley formula?
The Epley formula estimates 1RM as weight × (1 + reps ÷ 30). If you lift 100 kg for 5 reps, it estimates 100 × 1.1667 ≈ 117 kg. It is the most widely used 1RM formula in strength training.
How accurate are 1RM calculators?
Reasonably accurate for sets of 10 reps or fewer, usually within 5 to 10 percent. Accuracy drops with high-rep sets, and estimates vary by lift. Treat the result as a programming guide, not a guarantee of what you can lift.
Should beginners test their true 1RM?
No. True max attempts carry the highest injury risk and demand refined technique. Beginners get safer, more useful numbers from estimates based on sets of 5 to 10 reps, and should always use a spotter on heavy lifts.
How many reps are best for estimating 1RM?
Ten or fewer, taken close to failure with good form. Sets of 3 to 8 reps give the most reliable Epley estimates. Beyond 10 to 12 reps, muscular endurance skews the formula.
Is my data sent anywhere?
No. The calculator runs entirely in your browser. Nothing you enter is uploaded or stored.