The formula
How to calculate 1 rep max (bench)
A one-rep max is the heaviest weight you could lift for a single full repetition. Testing it directly on the bench press carries real risk, so this estimates it from a lighter set taken close to failure using the Epley formula.
Lifting 100 kg for 5 reps estimates a 116.7 kg max under this formula. Epley tends to run a few kilograms higher than the alternative Brzycki formula once rep counts climb past 8-10, which is why most lifters treat the output as a starting point rather than a guaranteed number.
What to enter:
- Weight lifted (kg) — the heaviest weight completed for the full set, not a warm-up
- Repetitions completed — accuracy drops above about 10-12 reps
Everything recalculates as you type, and the numbers in the address bar update with it, so a link to this page carries your figures with it.
If an exact figure for one of the fields is not available, a careful estimate is a reasonable starting point, since the calculator recomputes instantly the moment a more accurate number is available — nothing here depends on getting every field exact on the first pass.
Why 1 rep max (bench) matters
This kind of calculation gets used both out of general interest and ahead of a specific conversation — with a trainer, a midwife or a GP — where having an actual number ready, rather than a description, makes that conversation more concrete and specific.
It is most useful tracked over time rather than read once — a single reading tells you where you are today, while the same calculation repeated weeks or months apart, using the same method each time, shows the direction things are actually moving in.
None of the figures produced on this page are intended to replace a proper assessment, and nothing here should be read as a diagnosis or a treatment recommendation. What a calculator like this is good for is preparation — arriving at an appointment with an actual number already in hand, rather than a vague sense of a change, tends to make that conversation more useful for everyone involved.
Where a result depends on more than one measurement, small errors in each input tend to compound rather than cancel out — a slightly mismeasured waist and a slightly mismeasured height, taken together, can shift a derived figure more than either error would on its own. Taking each measurement carefully, and ideally twice, is worth the extra minute it takes.
Worked example
A concrete run-through, using the values already in the fields:
- Weight lifted: 100 kg
- Repetitions completed: 5
That gives:
- 1 rep max: 116.67 kg
Those starting figures exist only to show the calculation working, not as a target or a reference value to compare yourself against — replace them with your own measurements in the calculator above and the same formula applies exactly as shown.
Reading the result
Estimates are most reliable for sets of 1-5 reps and lose accuracy past about 10, since fatigue affects bar speed differently from one person to the next. Use the figure to set a conservative target — try 90-95% of the estimate for an actual max attempt.
Where this goes wrong. The set needs to be taken close to technical failure for the estimate to mean anything; if two or three reps were left in the tank, the true max is higher than the formula suggests. This is an estimate, not a substitute for a supervised max attempt with a spotter.
As with any general-purpose formula, the result here is an estimate derived from population averages, not a measurement specific to you — a reasonable starting point for a conversation with a qualified professional, not a replacement for one. Nothing on this page is medical advice.
Within about 5-10% for sets of 2-6 reps taken to or near failure. Below 2 reps or above roughly 10, the error grows because the relationship between reps and load stops being reliably linear.
No single formula wins for everyone — Epley and Brzycki are the two most used, and they agree closely for sets under 6 reps. A few kilograms of difference between formulas is normal and not worth chasing.
The headline figure is 1 rep max. With 100 kg weight lifted and 5 repetitions completed, that comes to 116.67 kg. Change any field and the figure moves with it.
It uses a published formula applied exactly as defined, so the arithmetic itself is precise — but the formula is a population-level estimate, and individual results can vary from it for reasons the formula has no way to account for. Treat the output as a reasonable estimate rather than a measured or diagnostic value.
For most people, yes — a single reading is a snapshot, while the same measurement repeated consistently over weeks or months shows a trend, which is generally more informative than any one figure taken in isolation.
Small differences between calculators usually come down to which published formula or reference dataset each one uses — several equations in this area exist in more than one accepted version. This page states the specific formula used in the section above, so it is possible to check directly whether another source is using the same one.