Enter the weight you lifted and how many reps you got (2–12). This calculator estimates your one-rep max with the Epley formula, compares it to Brzycki, and gives you a percentage chart for programming.
How the one rep max calculator works
Your one-rep max (1RM) is the most weight you could lift for a single rep with good form. You don't have to test it to know it: there's a reliable relationship between how much you can lift and how many times you can lift it. This calculator uses the Epley formula — the most widely used 1RM estimator — as the headline number, shows the Brzycki formula alongside it as a sanity check, and builds a training percentage chart so you can program your working sets.
The formulas
Epley: 1RM = w × ( 1 + r ÷ 30 )
Brzycki: 1RM = w × 36 ÷ ( 37 − r )
Here w is the weight you lifted and r is the number of reps you completed with it. Both formulas assume the set was taken close to failure — a comfortable 5 when you had 10 in the tank will underestimate your max.
Worked example
You bench 225 lbs for 5 reps:
Epley: 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lbs
Brzycki: 225 × 36 ÷ (37 − 5) = 8,100 ÷ 32 = 253.1 lbs
Your true max likely sits in the 253–263 lb range. For programming, 80% of the Epley estimate is about 210 lbs — a sensible load for working sets of 5.
Why the estimates diverge — and why we cap reps at 12
Epley and Brzycki were both fitted to real lifter data, but with different curves, so they agree almost perfectly around 2–6 reps and drift apart from there. Beyond about 10 reps the drift becomes a gulf, because high-rep sets test muscular endurance — your ability to buffer fatigue — more than maximal strength. Two lifters with identical 1RMs can differ by five or more reps at 70% of max. That's why this calculator caps input at 12 reps: past that, any formula is guessing. For the most trustworthy estimate, use a genuinely hard set of 3–5 reps. And if you decide to test your real 1RM, treat it like an event: full warm-up, progressive singles, a spotter or safety pins, and no grinding a rep that stalls.
Frequently asked questions
How do I calculate my one rep max without actually maxing out?
Take a recent hard set — say, the most weight you've lifted for 5 clean reps — and plug it into an estimation formula. The Epley formula (weight × (1 + reps/30)) is the most widely used. A 5-rep set at 225 lbs estimates a 1RM of about 262 lbs, no max-out attempt required.
Which is more accurate, Epley or Brzycki?
They agree closely in the 2–6 rep range and drift apart as reps climb — Brzycki runs a bit lower at higher reps. Neither is universally more accurate; it depends on the lift and the lifter. Use sets of 3–5 reps for the tightest estimates, and treat the two formulas as a plausible range rather than a single truth.
Why can't I enter more than 12 reps?
Above roughly 10 reps, muscular endurance starts driving performance more than maximal strength, and every 1RM formula loses accuracy fast — a 20-rep set says more about your conditioning than your max. We cap input at 12 to keep estimates honest. For the best estimate, use a heavy set of 3–5 reps.
How do I use 1RM percentages in my training?
Most programs prescribe loads as a percentage of your 1RM: roughly 80–90%+ for strength work in the 2–5 rep range, 70–80% for hypertrophy sets of 6–12, and 60–70% for technique and volume work. If your estimated 1RM is 262 lbs, a "5 reps at 80%" prescription means about 210 lbs.
Should I ever test my actual 1RM?
For most lifters, rarely — true max attempts carry the highest injury risk in the gym and interfere with training for days. If you do test, do it fresh, after a thorough warm-up with progressive singles, with a spotter or safety bars, and only on lifts where your technique is solid. Estimates are enough for programming.