How this one-rep max calculator estimates a max
A one-rep max (1RM) is the heaviest load you could lift once with acceptable form on a given day. Testing a true max is stressful and, for many lifters, unnecessary. A submaximal set — say five reps at a hard but controlled weight — can be run through a published estimator to sketch a max, then converted into training percentages.
This page uses four common formulas. Epley is weight × (1 + reps/30). Brzycki is weight × 36 / (37 − reps). Lander is 100 × weight / (101.3 − 2.67123 × reps). Lombardi is weight × reps^0.1. When you enter a single repetition, every formula simply returns that weight — there is nothing to estimate. The large number on the card is the average of the four, which keeps you from treating one author’s curve as a law of nature. The percentage table is built from that average.
The formulas do not agree perfectly, and they should not. They were fitted on different groups, lifts, and rep ranges. Agreement is usually closer at 2–6 reps than at 12–15. A set of 15 easy reps is a poor input; a near-limit set of 5 is a better one. If you grind the last rep with a big form break, you have not really “done” that rep in the sense these models assume.
Use the percentage chart as a starting load, not as a dare. Many programs write work sets at about 70–85% of a 1RM for strength or hypertrophy blocks. Your best load still depends on fatigue, sleep, range of motion, and the lift itself. A squat 1RM estimate should not be copied onto a deadlift, and a machine 1RM is not interchangeable with a free-weight 1RM.
This is an educational estimate. It is not a substitute for a coach, and it is not a reason to test a heavy single if you are injured, new to a lift, or lifting without a safe setup. If you want help picking daily calories around training, use the TDEE calculator and the protein calculator.
Frequently asked questions
Which formula should I trust?
None of them is a laboratory measurement. Epley and Brzycki are the two you will see most often. Showing four results plus an average is more honest than pretending one curve is official. If you already follow a program that specifies Epley or Brzycki, use that one so your loads match the author’s intent.
How many reps should I use?
A hard set in the 2–8 range is usually the sweet spot. Beyond about 10 reps the estimate often drifts. Do not use a warmup set; the formulas assume the set was taken close to the limit for that load.
Should I test a real one-rep max instead?
Only if you have a reason, a safe setup, and experience with heavy singles. Many lifters never need an official max. An estimated 1RM is enough to assign percentages. Skip max testing if you are injured, exhausted, or still learning the lift.
Why is my estimated max different from last month?
The estimate moves whenever the input set moves. It also cannot see fatigue or a better groove. Compare estimates taken under similar conditions — same lift, similar rest, similar depth or range — rather than chasing a new “PR” from a looser rep.
Can I use this for bench, squat, and deadlift?
Yes, but run each lift separately. Strength does not transfer one-for-one between lifts, and some people are relatively better at high-rep bench than at high-rep squats. Enter the set that belongs to the lift you want to program.