One Rep Max (1RM) Calculator
Estimate your one-rep max from a weight you can lift for multiple reps, and get a full percentage training chart.
How to use the one rep max calculator
- Enter the weight you lifted and how many reps you completed.
- Choose your unit (kg or lb).
- Click Calculate to see your estimated 1RM and percentage chart.
Using percentages to program your training
Many strength programs prescribe loads as a percentage of 1RM — for example 5 sets of 5 at 80%. The chart this tool produces lets you turn your estimated max into concrete working weights for each rep range.
Frequently asked questions
How is one-rep max calculated?
1RM is estimated from submaximal lifts using formulas like Epley (weight × (1 + reps/30)). This tool averages several validated formulas for a robust estimate.
How many reps should I use for an accurate 1RM?
Estimates are most accurate at 2–5 reps. Above about 10 reps, fatigue and technique reduce accuracy.
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