What a one-rep max is
Your one-rep max (1RM) is the heaviest weight you can lift for a single, full repetition of an exercise. It's the standard benchmark of strength and the foundation of most serious training programs, which prescribe work as a percentage of it.
You don't have to actually attempt a true max to know it. Lifting a submaximal weight for a few clean reps to failure lets a formula estimate your 1RM — safer and just as useful for programming.
How it's estimated
This calculator uses two of the most trusted equations and averages them:
- Epley: 1RM = weight × (1 + reps / 30)
- Brzycki: 1RM = weight × 36 / (37 − reps)
Both are most accurate when you test with 10 reps or fewer. The more reps you do, the more fatigue and technique drift creep in, so a heavy set of 3–6 gives the cleanest estimate.
Using the percentage table
The table shows what to load for different goals, all derived from your estimated max:
- Strength: 85–95% of 1RM for low reps (2–5).
- Muscle growth (hypertrophy): 67–85% for moderate reps (6–12).
- Endurance: below 67% for higher reps (12+).
Testing safely
Always warm up thoroughly with lighter sets first. If you ever attempt a true heavy single, use a spotter or safety bars and never sacrifice form for weight. Beginners are usually better off estimating from a set of 5–8 reps than attempting an all-out max.
Helpful tools
Support your core and brace harder on heavy sets.
View options →Track your lifts and watch your estimated 1RM climb.
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Frequently asked questions
How accurate is an estimated 1RM?
Very accurate when you use a set of 10 reps or fewer to failure. Estimates drift as reps climb, because fatigue and form breakdown distort the result.
What's the best rep range to test with?
A heavy set of about 3 to 6 clean reps to failure gives the most reliable estimate while keeping the risk low.
Should beginners max out?
No. New lifters should estimate their max from a submaximal set rather than attempting a true one-rep max, which carries more injury risk before technique is solid.
How often should I retest?
Every 4 to 8 weeks is plenty. Strength changes gradually, and frequent maximal testing adds fatigue without much extra information.