One Rep Max (1RM) Calculator
Estimate your one rep max from any set. Uses the Epley, Brzycki, and Lombardi formulas for accurate results.
What is a one rep max?
Your one rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with proper form. It's the standard measure of maximal strength, and most percentage-based training programs prescribe working weights as a percentage of it.
You don't need to actually test a max to know it. This calculator estimates your 1RM from any set you've performed — enter the weight and how many reps you got, and it applies three proven formulas. For best accuracy, use a set of 3–6 reps performed with good form to near failure.
Epley vs Brzycki vs Lombardi formulas
Epley: weight × (1 + reps/30). The most widely used formula. Best for moderate rep ranges (3–10); tends to estimate slightly high at very low reps.
Brzycki: weight × 36/(37 − reps). Most accurate for lower rep ranges (1–6); becomes conservative as reps climb.
Lombardi: weight × reps^0.1. Generally the most conservative of the three, especially at higher reps.
No single formula is right for everyone — they diverge more the further you get from 1 rep. The average of all three gives the most reliable estimate for most lifters, which is why this calculator shows it first.
How to use 1RM training percentages
Once you know your estimated 1RM, you can derive working weights for any goal: strength work typically lives at 80–95% of 1RM for 1–6 reps, hypertrophy at 65–80% for 6–12 reps, and muscular endurance below 65% for 12+ reps.
For example, with an estimated 1RM of 100 kg: 90% is 90 kg for around 3 reps, 80% is 80 kg for around 6 reps, and 70% is 70 kg for around 10 reps. Enter your own numbers above to get a full percentage table for your lift.
Loading the bar for these weights? Use the barbell plate calculator to see exactly which plates to put on each side. And if you want your estimated 1RM tracked automatically over time, read how to track progressive overload.
One rep max FAQ
How accurate are 1RM calculators?
For sets of 2–6 reps taken close to failure, formula-based estimates are typically within about 5% of a true tested max. Accuracy drops as reps go up — beyond 10–12 reps the estimate becomes much rougher, because fatigue resistance starts to matter more than pure strength.
Which 1RM formula is most accurate?
It depends on the rep range. Brzycki tends to be most accurate for low reps (1–6), Epley for moderate reps (3–10), and Lombardi generally produces the most conservative numbers. Averaging several formulas — as this calculator does — smooths out their individual biases.
Should beginners test a true one rep max?
Usually not. Testing a true 1RM is technically demanding and carries injury risk if your form breaks down under maximal load. An estimated 1RM from a hard set of 3–6 reps gives you the same programming information with far less risk.
How often should I recalculate my 1RM?
Every 4–6 weeks is plenty for most lifters, or whenever you set a meaningful rep PR. Your estimated 1RM should drift upward slowly — recalculating after every session just adds noise.
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