Plot No. 51 · Health & Fitness
One-Rep Max (1RM) Calculator
Estimate the most weight you could lift for a single rep from a set you have already done. Using the Epley formula, your one-rep max equals the weight lifted times one plus the reps divided by thirty. The calculator also breaks that max into useful training percentages.
Epley estimate from a sub-maximal set. It is most accurate for low rep counts and is a training guide, not medical advice.
The link saves your inputs so you can bookmark or share this exact result.
How your one-rep max is estimated
A one-rep max is the heaviest weight you could lift for a single repetition. Rather than risk an actual max attempt, this calculator estimates it from a set you have already completed using the Epley formula: 1RM equals the weight lifted times one plus the reps divided by thirty. So lifting 80 kg for 5 reps gives 80 times 1.1667, about 93 kg.
Brzycki is a well-known alternative formula that divides the rep count differently and tends to return a slightly lower max as reps climb. Both are reliable from low rep sets and drift apart at high reps. Once you have an estimated max, the calculator breaks it into the training percentages most programmes prescribe, from heavy singles down to higher-rep volume work.
How to use the one-rep max calculator
- Enter the weight you lifted, in kilograms.
- Enter how many clean reps you completed with that weight.
- Read your estimated 1RM and the table of working weights at 95, 90, 85, 80 and 70 percent.
Worked examples
A set of 5 at 80 kg
Inputs: 80 kg lifted for 5 reps
Result: Estimated 1RM of 93.3 kg. Working loads: 88.7 kg at 95 percent, 84.0 kg at 90, 79.3 kg at 85, 74.7 kg at 80 and 65.3 kg at 70 percent.
A heavy triple
Inputs: 100 kg lifted for 3 reps
Result: Estimated 1RM of 110 kg, from 100 times 1.1. The 85 percent strength load works out to 93.5 kg.
Limitations and common mistakes
Edge cases and limitations
- Accuracy is best for sets of about 2 to 6 reps; above 10 reps the estimate tends to overshoot.
- It assumes the reps were taken close to failure with good form, not easy or grinding reps.
- This is a training guide, not medical advice; warm up properly before lifting near these loads.
Common mistakes
- Plugging in a long, easy set of 15 and treating the inflated number as a true max.
- Forgetting to include the bar weight in the total weight lifted.
Frequently asked questions
How is one-rep max calculated?
This calculator uses the Epley formula: 1RM equals weight times one plus reps divided by thirty. Lifting 80 kg for 5 reps gives 80 times 1.1667, which is about 93 kg. An alternative is the Brzycki formula, which divides differently and tends to give a slightly lower number at high reps.
How many reps should I use for an accurate estimate?
Estimates are most reliable from sets of 2 to 6 hard reps. Above about 10 reps, fatigue and technique drift make every formula less accurate, so a 15-rep set will overstate your true single.
What are the training percentages for?
Most programmes prescribe work as a percentage of your max. Heavy strength work sits around 85 to 95 percent, while 70 to 80 percent builds muscle with more reps. The table turns your estimated max into those working weights.
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