Guide
How to Calculate Your 1RM
Quick answer
To calculate a one-rep max, take a hard set you already did, note the weight and the reps you completed, and run it through a published formula. One rep returns the weight you lifted. More reps return an estimate, not a tested single.
On this site the default is the average of Epley, Brzycki, Lombardi, Lander, Mayhew, O'Conner, and Wathen. Use that number for percentages. Do not treat it as the bar you must put on your back next week.
Estimates only. Testing a true max carries risk; use a spotter or safety arms. Not medical advice.
One rep max calculatorWeight, reps, seven formulas, and a percentage chart.Open →On this page
- How do you calculate a 1RM step by step?
- Which formula should the calculation use?
- What does a worked example look like?
- What if the set was not a max-effort set?
- When should you not trust the number?
- Key takeaways
- FAQ
How do you calculate a 1RM step by step?
Pick a set from the last few weeks that was actually hard, between about 3 and 6 reps. Write the load and the reps you finished. A set you stopped early on purpose is not the same as a set you took to the last clean rep.
Enter those two numbers in the one rep max calculator. Leave the formula on Average unless you have a reason to use one curve. Bench variations default to Mayhew. Conventional and sumo deadlifts default to Brzycki. Read the spread, not only the big number. The low and high formulas are telling you how much the equations disagree.
Round the training weight to the plates you own. A 2.5 kg jump is the usual kilogram increment. A 5 lb jump is the usual pound increment. The chart from 100% down to 50% is the part you take to the gym. The estimated max is just the input to that chart.
Which formula should the calculation use?
Epley is w × (1 + r / 30). Brzycki is w × 36 / (37 − r). The other five are on the formula comparison. They agree closely at 2 or 3 reps and drift apart as the set gets longer.
If you only want one equation and the lift is a bench, Mayhew is the curve that was fit on the bench press. If you want one number that does not hide the disagreement, use the average. Switching formulas to get a bigger max is not a strength gain.
What does a worked example look like?
Example only: 100 kg for 5 reps. Epley returns 100 × (1 + 5/30) = 116.7 kg, which this site rounds to the nearest 0.5 kg. Brzycki returns 100 × 36 / 32 = 112.5 kg. The average sits between the low and high of all seven. Your program should use a percent of that average, then round again to a load you can plate.
The same set in pounds is a different display, not a different formula. The conversion used here is 1 lb = 0.45359237 kg. Do the math in one unit and convert at the end if you have to talk about both.
What if the set was not a max-effort set?
A calculator assumes the reps you typed were as many as you could do at that weight. If you left two reps in the tank, the estimate is low. The optional RPE toggle on the homepage adds the difference from 10 to your reps. Five reps at RPE 8 is treated as seven effective reps. That is a simple adjustment, not the full RPE chart.
Better: log the set as it happened and do not invent reps. A clean set of 5 at a known RPE is more useful next month than a guessed single.
When should you not trust the number?
Above 10 reps the page warns you. Above 20 it will not calculate. Olympic lifts are worse still. A snatch estimate from reps is a weak forecast. Machine and isolation work can use higher reps, and the number is still only for that machine, that seat, and that range.
LeSuer and colleagues found high correlations between predicted and tested maxes in untrained students, and they still found systematic misses. High correlation is not a promise that your next single will match the screen.
Key takeaways
- Use a hard set of about 3–6 clean reps.
- Write down the formula so next month matches.
- Round the training load to plates, not to the raw estimate.
- A sloppy set produces a sloppy max.
FAQ
Does a 1RM calculator replace a test?
No. It estimates a single from a submaximal set. A test is the only way to know the single. Most training does not need the test.
What if I only did one rep?
The calculator returns the weight you entered. There is nothing to estimate.
Should I use the highest formula?
No. The high end is the optimistic equation for that set. Programming off the high end is how you miss the first work set.
Can I calculate a dumbbell 1RM?
Yes. Enter the weight of one dumbbell. The result is for one dumbbell, not a barbell equivalent.
Where do the percentages come from?
They are fractions of the estimated max. Approximate reps at each percent come from the inverse of the formula you selected, not from a separate study.