How to use
- 1Enter the weight you lifted and the reps you completed (1–12); pick kg or lb.
- 2Read the result of seven formulas, the average 1RM and the spread between them.
- 3If the set was not to failure, select its RPE to get an RPE-based 1RM as well.
- 4Plan your working weights with the 50–100 % chart and the RPE/RIR chart.
The 1RM formulas: Epley, Brzycki and more
The calculator runs seven established equations side by side: Epley (1985), Brzycki (1993), Lombardi (1989), Mayhew (1992), O’Conner (1989), Wathan (1994) and Lander (1985). For example, 100 kg × 5 reps gives 116.7 kg with Epley and 112.5 kg with Brzycki. The formulas agree closely between 1 and 10 reps and drift apart above that, so the most reliable estimate comes from a heavy set of 3–6 reps. It is still an estimate: test a true max only when fully warmed up, with solid technique and a spotter.
Percentage chart and RPE / RIR
The percentage chart lists 50–100 % of your average 1RM rounded to plates (2.5 kg or 5 lb), with an approximate rep count from the inverse Epley formula. The RPE chart follows the widely used table by powerlifting coach Mike Tuchscherer (RTS): RPE 10 means no reps left, RPE 8 means two more were possible (RIR 2). Five reps at RPE 8 is about 81.1 % of your 1RM, and the tool uses that to give a second 1RM estimate.
Using it in training
Strength blocks usually sit at 80–90 % for 2–5 reps; hypertrophy work at 65–80 % for 6–12 reps. Rather than maxing out every session, take an estimate from a heavy set every few weeks — it is safer and just as useful for programming. If you have pain, an injury or a health condition, check with a doctor before heavy lifting; this tool is not medical advice.
Frequently asked questions
How do you calculate your one rep max?
The most common method is Epley: 1RM = weight × (1 + reps ÷ 30). 180 lb × 8 reps gives about 228 lb. This tool averages seven formulas.
Which 1RM formula is most accurate?
There is no single winner. Brzycki and Epley are almost identical at low reps, and Mayhew and Wathan performed well in bench press studies. The average and the spread show how much to trust the estimate.
What does RPE 8 mean?
You finished the set with two reps left in the tank (RIR 2). RPE 10 is an all-out set; RPE 9 leaves one rep in reserve.
What percentage of my 1RM should I train at?
Typically 80–90 % for 2–5 reps for strength and 65–80 % for 6–12 reps for muscle growth. The percentage chart shows those loads directly.
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