One Rep Max (1RM) Calculator
Estimate your one-rep max from a recent set using six common formulas (Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathen).
What this calculates
Your one-rep max (1RM) is the heaviest weight you could lift once with good form. Most lifters don't actually test this — too risky — and instead estimate from a submaximal set using rep-to-1RM formulas. This calculator shows results from six widely used formulas so you can see the range and pick a planning number.
Formula & how it works
Epley: 1RM = w × (1 + r/30). Brzycki: 1RM = w × 36 / (37 − r). Lombardi: 1RM = w × r^0.10. Mayhew: 1RM = w × 100 / (52.2 + 41.9 × e^(-0.055r)). O'Conner: 1RM = w × (1 + r/40). Wathen: 1RM = w × 100 / (48.8 + 53.8 × e^(-0.075r)). w = weight, r = reps performed. Formulas diverge above 10 reps — accuracy drops outside the 3–10 rep range.
Worked example
Squatted 225 lb × 5 reps to near failure. Epley: 225 × (1 + 5/30) = 262.5 lb. Brzycki: 225 × 36/32 = 253.1 lb. Lombardi: 225 × 5^0.10 = 263.3 lb. Range is roughly 253–263 lb — pick the lower end for planning if you're new to a lift, the average if you have experience.
Frequently asked questions
Which formula is most accurate?
All are within 5 % for trained lifters in the 3–8 rep range. Brzycki tends to be the most conservative; Epley the most generous. Pick one and stick with it for consistent trend tracking.
Should I test my actual 1RM?
Rarely. Even competitive lifters test in meets only a few times a year. Estimated max is fine for programming — no spinal compression risk, no chance of bailing out, no need for spotters.
What's a percentage-based program?
Many programs prescribe sets at 75 % of 1RM, 85 %, etc. The estimated 1RM is what you plug in. Most go up by 5 % every 2-4 weeks as strength builds.
When does this stop working?
Above 12-15 reps, formulas drift because muscular endurance starts dominating over strength. 1-3 rep tests are too short to compute confidently from. Best in the 3–10 rep zone.
Disclaimer: Use proper form and a spotter on max attempts. Talk to a coach if you're new to strength training.