1RM Calculator
Find your one-rep max or pick the right weight for your working sets — based on what you actually lifted.
Enter your lift
For decimals, type directly into the number field.
Don't train at your repmax. For efficient training, always leave 1–2 reps in reserve. Use the working set mode below for safe training weights.
Your estimated max
1 Rep Max
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kg · estimated max for 1 rep
2 RM
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3 RM
—
5 RM
—
10 RM
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Working set weights
Leaving 1–2 reps in reserve (RPE 7–8)
Strength · 3–5 reps
~90% of 1RM
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Power-hypertrophy · 5–8 reps
~80% of 1RM
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Hypertrophy · 8–12 reps
~70% of 1RM
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Endurance · 12–15 reps
~60% of 1RM
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How the 1RM formula works
This calculator uses the Wathan formula, one of the most accurate multi-rep prediction models for real-world lifting.
Enter any set
Use a weight you can lift with good form for 1–12 reps. Avoid grinding reps — clean technique gives the best estimate.
Formula runs instantly
The Wathan formula calculates your estimated 1RM and derives all nRM values from a validated percentage table.
Read your numbers
See your theoretical max and working set weights for every major training zone — strength, hypertrophy, endurance.
1RM estimates are approximations. Factors like fatigue, exercise selection, bar speed, and training age affect your real max. Use the result as a training guide, not an absolute number. Never attempt a true 1RM without a spotter.
A number today. A PR next month.
SlayCal logs your lifts and tracks strength progress over time — so you always know if you're getting stronger.
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