One Rep Max Calculator
Estimate the heaviest weight you could lift once for a given exercise from a set you completed, using the Epley formula on your weight and rep count.
Recent
Formula
How the calculation works
Enter the weight you lifted in kilograms and the number of clean repetitions you completed in that set, and the tool applies the Epley formula to estimate your single-lift maximum.
The formula multiplies your working weight by one plus the rep count divided by thirty, so a set of five adds roughly one sixth to the weight you actually moved.
The result estimates the heaviest load you could move once with good form, which is useful for setting percentages in a structured strength programme.
Common mistakes
- Using a set taken close to failure with sloppy form, because the Epley estimate assumes every repetition was a full and honest rep.
- Applying the formula to a set of fifteen or twenty reps, where the estimate becomes optimistic and can overshoot the weight you really can lift.
- Treating the number as a tested maximum and loading it immediately, rather than building up to it gradually with warm-up sets and a spotter.
When to use it
- Use it to pick training percentages, since most strength programmes ask you to work at a share of your one rep max rather than a fixed weight.
- Use it to track progress when you cannot safely test a true single, because a five rep set keeps giving a comparable estimate.
Worked example
Lifting 80 kg for 5 reps gives an estimated one rep max of about 93.33 kg, because 80 multiplied by 1 plus 5 divided by 30 equals 93.333.
Common questions
How accurate is the Epley formula?
It is most reliable between about 2 and 10 repetitions; outside that range the estimate drifts, so treat the result as a guide rather than a tested max.
Should I try to lift this weight right away?
No, the number is an estimate; build up to it across several sessions with warm-up sets and a spotter before attempting a true single.
Related tools
-
Discount Calculator
See what you actually pay after a discount, and how much you save.
-
Tip Calculator
Add a tip to the bill and split it between people.
-
Add Tax / VAT Calculator
Add tax or VAT to a price to get the total.
-
Percentage Calculator
Find what percentage one number is of another.
-
Percentage Change
How much a number rose or fell between two points.
-
Monthly Budget Split
Divide monthly income into needs, wants and savings.
-
Profit Margin & Markup
Profit, margin and markup from a cost and a selling price.
-
Original Price from a Sale
Work back from a discounted price and the discount rate to the original.