What Is a 1RM Calculator?
Your one-rep max (1RM) is the heaviest weight you can lift for a single
full repetition of an exercise with correct form. Testing it directly is
risky and fatiguing, so most lifters and coaches estimate it instead using
a rep-max formula. This calculator supports two of the most widely used
formulas:
Epley formula: 1RM = weight × (1 + reps ÷ 30)
Brzycki formula: 1RM = weight × 36 ÷ (37 − reps)
Both formulas assume a fairly direct relationship between the weight you
move and how many clean reps you can complete with it. They work best for
sets of 1 to 10 reps on compound barbell lifts such as the squat, bench
press, and deadlift.
How to Use This Calculator
Enter the heaviest weight you lifted for a clean set, along with how many
reps you completed before reaching failure. For the most reliable
estimate, use a set of 10 reps or fewer — accuracy drops for higher-rep
sets. The calculator also shows common training percentages (70%, 85%,
and more) so you can plan your next session's working weights directly
from the result.
Frequently Asked Questions
What is a 1RM calculator?
It estimates the maximum weight you could lift once, based on a lighter weight lifted for multiple reps.
How accurate is a 1RM calculator?
Typically accurate within 5-10% for sets of 1-10 reps. Accuracy drops for higher rep counts.
Which formula is most accurate: Epley or Brzycki?
Epley runs slightly higher above 5 reps; Brzycki is often more precise under 10 reps.
Should I test my true 1RM instead?
Only with a spotter and proper warm-up — most lifters get more value from an estimate for planning training percentages.