1RM Calculator — One Rep Max
Estimate your one rep max from any weight and rep count. Get your full training weight table by percentage.
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📘 What is the 1RM Calculator — One Rep Max?
Your one-rep max (1RM) is the heaviest weight you could lift for a single rep with good form — useful for programming training percentages, but risky to actually test directly for most lifters. This calculator estimates it from a safer, sub-maximal set using five established formulas, then shows training weights at each percentage of that estimate.
⚙️ How 1RM / One Rep Max is calculated
Why estimate instead of testing directly
Testing a true 1RM requires a near-maximal, high-risk single lift, ideally with a spotter and a coach present. Estimating from a moderate-weight set of 3–8 reps is far safer and, for most lifters, accurate within a few percent of the true value.
Why this calculator averages five formulas
Epley, Brzycki, Lombardi, Mayhew, and O'Conner were each derived from different research samples and rep ranges. No single formula is consistently most accurate across all rep ranges and lifters, so averaging across all five smooths out the idiosyncrasies of any one formula.
Why accuracy drops above 12 reps
All rep-max formulas become less reliable as rep count rises, since high-rep sets are increasingly limited by muscular endurance and fatigue rather than pure strength.
Epley formula
1RM = weight × (1 + reps ÷ 30)
Brzycki: weight × 36 ÷ (37 − reps)
🧮 Worked examples
Example — 80kg for 6 reps
A lifter completes 80kg for 6 reps with good form on the final rep.
→ Epley estimates ≈96.0kg; Brzycki estimates ≈92.9kg — both formulas cluster within about 3% of each other
Example — using the result for programming
Average estimated 1RM of 94kg. Programming a hypertrophy-focused session at 75–80% of 1RM.
→ Target working weight ≈70.5–75.2kg, typically performed for 6–8 reps per set
💡 Original insights & how to use this calculator
Programming training percentages without testing a true max
Strength programs are often written as percentages of 1RM. This calculator lets you derive that baseline from a safe, sub-maximal set rather than risking a true maximal test.
Tracking strength progress over time
Recalculating your estimated 1RM every few weeks from your current working sets shows whether your strength is genuinely progressing, even if you never test an actual single-rep max directly.
Choosing the right rep range for your specific goal
The percentage table shows roughly which rep range corresponds to each training goal — heavy, low-rep work for max strength, moderate weight and reps for hypertrophy, lighter weight and higher reps for muscular endurance.
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💡 Expert tips
Use 3–8 reps for best accuracy — 1RM formulas are less reliable above 10 reps.
80% of 1RM for 8 reps is ideal for muscle growth.
Re-test 1RM every 4–6 weeks as strength improves.
📖 Learn more on WellFiLab
Visit ↗❓ Common questions
Which 1RM formula is most accurate?
Epley and Brzycki are most widely used. Average all five for the best estimate.
Should I test my actual 1RM?
Only with a spotter and proper warm-up. For most people, a calculated estimate is safer.
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