One Rep Max Calculator
Estimate your 1RM (one repetition maximum) for any lift using weight and reps performed. Calculate training percentages for programming.
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How to use this calculator
w = weight lifted; r = number of reps completed with that weight. The tool applies it to any rep count from 1 upward; it is a rough fit for sets of about 2 to 10 reps.
- 1
Enter the weight you lifted and pick kg or lbs.
- 2
Enter the number of repetitions you completed with it.
- 3
Read the estimated one-rep max from the Epley formula.
- 4
Use the 95% to 70% rows to pick working weights, rounded to the plates you own.
Frequently asked questions
What is a one-rep max (1RM)?
It is the heaviest load a lifter can move for one repetition. This tool does not measure it; it estimates it from a set you already did, then lists fixed percentages of the estimate so you can choose loads for later sessions.
Which formula does the tool use?
Epley only: 1RM = weight × (1 + reps ÷ 30). For 100 kg and 5 reps that is 100 × (1 + 5 ÷ 30) = 116.7 kg. The constant 30 is built into the tool, and the result is shown to one decimal place in the unit you picked.
What happens with 1 rep?
The tool returns the weight you typed, unchanged, with a note that it is already your max. No percentage rows are listed in that case, so a single-rep entry of 140 kg gives only “140 kg”.
What if I enter fractional reps, or zero?
Reps are rounded to the nearest whole number first, so 2.6 becomes 3 and 100 kg gives 110.0 kg. A rep count below 1, including an emptied box, returns the message “Reps must be at least 1”. A weight of 0 or less, including an emptied box, returns “Weight must be positive”.
Is there an upper limit on reps?
No. Epley is applied to any whole number from 2 upward, so 80 kg for 30 reps returns 160.0 kg, double the lifted weight. The formula was fitted to modest rep counts, so very high-rep entries produce arithmetic rather than a dependable estimate.
Do kg and lbs get converted?
No. The unit dropdown only changes the label printed after each number. Entering 225 with lbs gives 285.0 lbs for 8 reps, and entering 225 with kg gives 285.0 kg, because the same maths runs either way.
How do Brzycki and Lander compare?
This tool does not use them. For 100 kg × 5 reps, Brzycki (weight × 36 ÷ (37 − reps)) gives 112.5 kg and Lander (weight ÷ (1.013 − 0.0267123 × reps)) gives about 113.7 kg, against the 116.7 kg shown here. Compare estimates only within one formula.
Is this medical or coaching advice?
No. It estimates a number from the figures you give it and cannot judge technique, injury or health. A qualified coach or a medical professional should guide anyone with a condition or an injury before they choose loads.
1RM calculator — estimate your one-rep max and training weights
How the estimate is calculated
The tool applies the Epley formula, one rep max = weight × (1 + reps ÷ 30). It rounds the rep count to a whole number, multiplies, and prints the estimate with one decimal. It then prints six lines at 95%, 90%, 85%, 80%, 75% and 70% of that estimate. The unit choice only relabels the output; no kg-to-lbs conversion happens. Rounding is for display only, and each percentage row is computed from the unrounded estimate. Doubling the weight at the same reps doubles every line in the list.
Four runs of the calculator
These rows come from live runs of the calculator. The last row shows the whole-number rounding of reps: 2.6 is treated as 3.
| Entry | Estimated 1RM | 90% | 80% | 70% |
|---|---|---|---|---|
| 100 kg × 5 | 116.7 kg | 105.0 kg | 93.3 kg | 81.7 kg |
| 225 lbs × 8 | 285.0 lbs | 256.5 lbs | 228.0 lbs | 199.5 lbs |
| 60 kg × 12 | 84.0 kg | 75.6 kg | 67.2 kg | 58.8 kg |
| 100 kg × 2.6 | 110.0 kg | 99.0 kg | 88.0 kg | 77.0 kg |
Reading the full percentage list
For the 100 kg × 5 entry the tool lists 110.8, 105.0, 99.2, 93.3, 87.5 and 81.7 kg at 95% down to 70%. These are plain multiples of 116.7 kg, shown to one decimal, so the bar loads you actually use will differ by the plate increments available to you. The 60 kg × 12 row in the table above shows the higher-rep case: the same divide-by-30 term adds 40% to the lifted weight and reports 84.0 kg. Re-entering a newer set gives a fresh estimate; nothing is stored between visits.
Edge cases as coded
One rep returns your entered weight and skips the percentage list. Zero or an emptied reps box gives an error message, and so does a weight of zero or less. There is no ceiling on reps, so 30 reps doubles the weight; the maths is valid but the formula was never meant for such sets. Comparing Epley with other formulas such as Brzycki shows they differ by a few percent, so stick to one when tracking.
What the tool does not do
It cannot assess form, fatigue, injury or suitability for any person, and it is not medical advice. It also does not recommend how many sets, reps or percentages to train. A qualified coach, and for health concerns a doctor, decides what is appropriate for a particular lifter; the output here is just arithmetic on two numbers. Because only weight and reps go in, two lifters entering the same set get the same estimate whatever the exercise, bodyweight or training history.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →