Iron Log / Tools / 1RM Calculator
Free Tool

One Rep Max
Calculator

Enter the weight you lifted and how many reps you completed. We'll estimate your 1RM and show your full training zone table.

kg

Quick select reps

Estimated 1RM

133 kg

Epley

116.7 kg

Brzycki

115.7 kg

Training Zones

% 1RM Weight Rep Range

Formula: Epley (weight × (1 + reps÷30)). Best for 2–12 reps. Not valid for actual 1RM attempts.

How the Calculator Works

This calculator uses the Epley formula as the primary estimate: 1RM = weight × (1 + reps ÷ 30). The Brzycki formula is shown for reference: 1RM = weight × 36 ÷ (37 − reps). Results are rounded to the nearest 0.25 to match standard plate increments.

Which Formula Is More Accurate?

Epley is the most widely cited and performs well across rep ranges of 2–12. Brzycki tends to be more accurate at lower rep ranges (1–6 reps). Both become increasingly unreliable above 10 reps. For maximum accuracy, estimate from sets of 3–6 reps where you still have a rep or two left in the tank.

How to Use Your 1RM for Programming

Once you have your estimated 1RM, use the training zone table to set working weights for each session:

  • 85–100% Maximal strength. 1–5 reps. High CNS demand — limit to 1–2 sessions per week per lift.
  • 75–85% Strength-hypertrophy. 4–8 reps. The sweet spot for most strength programs.
  • 65–75% Hypertrophy. 8–12 reps. High volume, moderate weight.
  • Below 65% Endurance / technique work. 12+ reps.

Frequently Asked Questions

What is a one rep max? ↓
A one rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with proper form. It's the standard measure of absolute strength and is used to calculate working weights as a percentage of your maximum.
Should I actually test my 1RM? ↓
For most people, estimating from a heavy set of 3–6 reps is safer and nearly as accurate as a true 1RM attempt. Maximal singles increase injury risk, require full warm-up protocol, and aren't necessary for programming. Use this calculator regularly from your working sets instead.
Why are my Epley and Brzycki results different? ↓
The two formulas use different mathematical models and diverge more at higher rep counts. Epley tends to produce slightly higher estimates at higher reps. The true answer lies somewhere in the middle. If your set was 5 reps or fewer, both should be very close.

Track your 1RM over time

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