How the 1-rep max estimate works
Your one-rep max (1RM) is the most you can lift for a single rep. The Epley formula estimates it from a lighter set: 1RM = weight × (1 + reps ÷ 30). Lifting 100 kg for 5 reps gives about 117 kg. The estimate is most accurate for sets under about 10 reps.
Worked example: 80 kg for 8 reps gives 80 × (1 + 8 ÷ 30) = 101.3 kg. One extra rep moves the estimate by about 3% of the weight on the bar, so the reps you enter have to be genuine full-range reps taken close to failure — a grinding, half-locked last rep quietly inflates the number.
The same numbers feed straight into the kg to lbs calculator.
For the same task from a slightly different angle, try the VO2 max calculator.
How to use this calculator
Enter the weight you lifted and the reps you completed with good form. The result is your estimated 1RM, plus rough loads for 3 and 8 reps. Use it to plan training percentages — and always lift with a spotter when testing heavy.
The usual training percentages of 1RM are roughly 95% for a double, 90% for 3 reps, 85% for 5, 80% for 8 and 75% for 10. On a 117 kg estimate that works out at about 111, 105, 99, 94 and 88 kg respectively.
Re-run the estimate every four to six weeks rather than after one good session, since sleep, food and stress swing day-to-day performance more than most lifters expect.
Once that is settled, the lbs to kg calculator takes care of the next part.
Frequently asked questions
- How do I calculate my one-rep max?
- Use the Epley formula: 1RM = weight × (1 + reps ÷ 30). 100 kg for 5 reps is about 117 kg.
- How accurate is a 1RM estimate?
- It's reliable for sets of about 2–10 reps. Beyond that, fatigue makes the estimate less precise.
- Should I actually test my 1RM?
- Estimating from a submaximal set is safer. If you do test a true 1RM, warm up thoroughly and use a spotter.
- What is 90% of my 1RM for?
- It's roughly a 3-rep load, useful for strength training. About 80% is roughly an 8-rep load.
- Does the same estimate work for every lift?
- Not equally well. Squats and deadlifts use large muscle groups and usually allow more reps at a given percentage, so the formula tends to understate them, while bench and overhead press estimates land closer to reality.