How 1RM is calculated
Your one rep max, 1RM, is the heaviest weight you can lift once with clean technique. It can be estimated from a submaximal set with a formula. The Epley formula (1985) is weight × (1 + reps / 30), the Brzycki formula (1993) weight × 36 / (37 − reps) and the Lander formula (1985) 100 × weight / (101.3 − 2.67123 × reps).
The formulas agree closely for 1-5 reps and start to diverge on longer sets: Epley estimates slightly higher, Brzycki lower. That is why the calculator shows all three and the average. The SisuLift app uses the Epley formula in its reports.
How to use 1RM in training
The most common use is percentage-based programming: strength sets of 3-5 reps at about 85-90 percent, hypertrophy sets of 8-12 reps at about 70-80 percent. The percentage table gives weights directly; the working weight calculator also accounts for an RIR target.
Estimated 1RM moves day to day with sleep, recovery and technique. Treat it as a guide, not a law: if an 85 percent set feels like 95, listen to your body. You never need to test a true max; logged working sets are enough for tracking.
Frequently asked questions
What is 1RM?
1RM (one repetition maximum) is the heaviest weight you can lift once with proper technique. It is used as a measure of strength and as the basis for calculating training weights.
Which 1RM formula is the most accurate?
From sets under five reps all three formulas land within a few percent. On longer sets Brzycki is usually the most conservative and Epley the most optimistic. The average is a good compromise, and in the end your actual lift decides.
How accurate is a 1RM calculator?
In research the formulas typically land within 5 percent of a true max when the set is 1-6 reps and taken close to failure. From sets above 10 reps the error grows, because endurance starts to matter alongside strength.
Is testing your 1RM safe?
For an experienced lifter with a good warm-up and a spotter, yes, but it is not necessary. An estimated 1RM from a 3-5 rep set is enough for almost all programming, and it is the safer route, especially for beginners.
How many reps can you do at each percentage?
Roughly: 90 % about 3-4 reps, 85 % about 5-6, 80 % about 8, 75 % about 10 and 70 % about 12. Individual differences are large: an endurance-type lifter gets more reps at the same percentage than a strength-type lifter.
Does SisuLift calculate 1RM automatically?
Yes. The app estimates 1RM with the Epley formula from every logged working set and shows progress by exercise in the monthly report. You never need to test a max separately.