Free Tool — Personal Training
One-Rep Max Calculator
Estimate your one-rep max from any submaximal set and see your training-load percentages. Core programming math on the NASM, ACE, and ISSA personal trainer exams.
One-Rep Max Calculator
Most accurate at 10 reps or fewer.
Training Loads (% of 1RM)
Formula Reference
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
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How One-Rep Max Estimation Works
A one-rep max (1RM) is the most weight you can lift for a single repetition. Rather than testing a true max — which carries injury risk — trainers estimate it from a submaximal set using validated formulas.
This tool averages the two most widely taught equations: Epley (1RM = weight × (1 + reps ÷ 30)) and Brzycki (1RM = weight × 36 ÷ (37 − reps)). Estimates are most accurate at 10 reps or fewer; beyond that the formulas diverge and over-predict.
Certification exams test this because program design prescribes intensity as a percentage of 1RM — strength work at 85–95%, hypertrophy at 67–85%, and muscular endurance below 67%.
Frequently Asked Questions
How accurate is a 1RM estimate?
Most accurate when the set is 10 reps or fewer. At higher rep counts the formulas over-predict because strength-endurance varies more between people. For programming, use a set in the 3–8 rep range.
Should I use Epley or Brzycki?
Both are standard and taught on the major exams. Epley trends slightly higher at higher reps; Brzycki is close at low reps. This tool shows both and averages them for a balanced estimate.
Why do trainers use a percentage of 1RM?
Programs prescribe load as a percent of 1RM to target a goal: strength (85%+), hypertrophy (67–85%), or muscular endurance (under 67%). Knowing the 1RM lets you assign the right working weight.
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