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One Rep Max Calculator

Know your max without testing your max.

Testing a true one-rep max is fatiguing, risky, and unnecessary for programming. This calculator estimates your 1RM from any submaximal set using the two most validated formulas — Epley (the NSCA standard) and Brzycki — averages them for a robust estimate, and generates the full percentage chart that percentage-based programs (5/3/1, Texas Method, most powerlifting peaking plans) are built on.

Why people use this

Lifters use this every training day: percentage-based programs (5/3/1, most powerlifting plans) need a max to compute working weights, and testing a true 1RM is fatiguing and risky. Trainers use it to program for clients without ever maxing them out.

How it works

1. Enter the weight you lifted and the reps you completed with good form.
2. Sets of 1–12 reps give the most accurate estimates; accuracy drops beyond that.
3. The calculator applies Epley (weight × (1 + reps/30)) and Brzycki (weight × 36/(37−reps)) and averages them.
4. Read your estimated 1RM and the 50–95% training loads below it.

Common questions

How accurate are 1RM formulas?

Within roughly ±5% for sets of 5 reps or fewer on big barbell lifts, and ±10% for sets up to 12. Accuracy degrades on high-rep sets and isolation movements. Treat the number as a programming guide, not a guarantee.

Which formula do certifications like NASM and NSCA use?

The NSCA teaches the Epley formula; NASM materials commonly reference Brzycki. Both appear in this calculator — the averaged estimate is usually closest to a tested max.

How do I use the percentage chart?

Match the program to the row: strength work lives at 85–95% (1–5 reps), hypertrophy at 65–85% (6–12 reps), and muscular endurance below 65%. Recalculate every 4–8 weeks as your estimated max climbs.

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