One-Rep Max Calculator
Estimate your one-rep max from a recent set — no max-out attempt needed — plus the training weights for common rep ranges.
Example: with Weight lifted 185 · Reps performed 5 → Estimated 1-rep max: 216 lb.
Computed by the calculator below using its default values. Change any input to see your own numbers.
Training loads by % of 1-rep max
Strength training apps and programs
Learn moreEstimate without maxing out
Testing a true one-rep max is risky and taxing, so lifters estimate it from a lighter set taken near failure. Your 1RM then anchors training: most programs prescribe a percentage of 1RM for a given rep range, so knowing the number lets you load the bar correctly.
No single formula is exactly right for every lifter, so this calculator shows four widely used estimates side by side — Epley, Brzycki, Lombardi and O’Conner — from the same weight and reps you enter above. They are independent curve-fits to real lifting data, so they agree closely at low rep counts and spread apart as reps climb.
How it’s calculated & sources
The main result uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). The percentage table shows typical training loads for 2 to 12 reps, scaled off this Epley estimate.
The three additional rows use other commonly cited formulas, all solving for the same 1RM from your weight and reps: Brzycki: 1RM = weight × 36 ÷ (37 − reps); Lombardi: 1RM = weight × reps0.10; O’Conner: 1RM = weight × (1 + 0.025 × reps). Each is an empirical curve-fit to real lifting data with slightly different assumptions, which is why they don’t return identical numbers — Epley and Brzycki actually return the same value at exactly 10 reps, then diverge above and below it.
The %-of-1RM table maps each percentage to a typical rep range using a standard, widely cited strength-training correspondence (roughly 100%=1 rep, 95%=2, 90%=4, 85%=6, 80%=8, 75%=10, 70%=12, 65%=15, 60%=18, 55%=20, 50%=22+). This mapping is a general training guideline, not an exact law of physiology — individual fatigue resistance varies.
Benchmark: Epley and Brzycki are the two most widely used formulas and are considered reasonably reliable for sets of roughly 1–10 reps; all formulas lose accuracy above about 12 reps, so for the best estimate, test with a weight you can lift for 10 reps or fewer.
Results update as you type and are general estimates, not personalized financial, tax, medical or legal advice. Verify with a professional.
Worked example
Lifting 185 lb for 5 reps estimates a 1RM of about 216 lb — so roughly 173 lb for a set of 8 (80%).
Frequently asked questions
How many reps should I use?
Fewer reps (3–6) give the most accurate estimate. High-rep sets understate your true max because fatigue dominates.
Should I actually attempt my 1RM?
Only with experience, a spotter and proper warm-up. The estimate is safer for programming and works well for most lifters.
Why do the four formulas give different numbers?
Epley, Brzycki, Lombardi and O’Conner are each empirical curve-fits to real lifting data, built with slightly different assumptions about how strength falls off with reps. They agree closely for low-rep sets and spread apart at higher rep counts, so treat the differences as the normal margin of error in any estimate rather than a sign something is wrong.
Which formula is most accurate?
Epley and Brzycki are the most widely used and are considered reasonably reliable from about 1 to 10 reps — they even return identical results at exactly 10 reps. Above roughly 12 reps, all formulas become less reliable, so for the best estimate, test with a weight you can lift 10 times or fewer.