How the 1RM calculator works
Your one-rep max (1RM) is the most weight you can lift for a single clean rep. Testing it directly is fatiguing and carries more injury risk — especially after 40 — so this calculator estimates it from a submaximal set with the Epley formula:
1RM = weight × (1 + reps ÷ 30)
For example, 225 lb for 5 reps gives 225 × (1 + 5/30) ≈ 263 lb.
Getting an accurate estimate
Prediction formulas are most accurate with heavier sets of about 3–10 reps taken close to failure. Above 10 reps, the estimate gets less reliable because muscular endurance starts to matter as much as strength. Use a set with good form where you had no more than one or two reps left in the tank.
Using the percentage table
The table translates your estimated 1RM into working weights. Most strength programs are written as percentages: roughly 85–90% for sets of 2–6 (strength), 70–80% for 6–12 (muscle growth), and 60–65% for 12–20 (endurance and technique). For lifters over 40, spending most training time in the 65–85% range builds strength with less joint stress than frequent max attempts.
Frequently asked questions
What is the Epley formula?
The Epley formula estimates one-rep max as weight × (1 + reps/30). It is one of the most widely used 1RM prediction equations.
How many reps should I use to estimate my 1RM?
Sets of about 3–10 reps taken close to failure give the most reliable estimate. Accuracy drops for sets above 10 reps.
Should I test my true one-rep max after 40?
It is not necessary for most people. An estimated max from a hard set of 3–5 reps is accurate enough to program training and carries less injury risk than a true max attempt.
Why is my estimate different from other calculators?
Different formulas (Epley, Brzycki, Lombardi and others) give slightly different numbers, especially at higher rep counts. Stick with one formula so your progress is comparable over time.