What is a 1RM?
Your one rep max (1RM) is the heaviest weight you can lift for a single complete repetition with proper form. It is the gold standard for measuring absolute strength in powerlifting and weightlifting.
Why estimate your 1RM?
Testing a true 1RM is risky. Heavy singles place extreme stress on your joints, spine, and connective tissue. Estimating your 1RM from a submaximal set is safer and still accurate enough for program design.
The three most accurate formulas
1. Epley Formula
The Epley formula is the most widely used 1RM estimator:
1RM = Weight × (1 + Reps / 30)
Example: 80 kg for 8 reps → 80 × (1 + 8/30) = 101.3 kg
2. Brzycki Formula
The Brzycki formula is more conservative and often preferred for higher rep ranges:
1RM = Weight × 36 / (37 - Reps)
Example: 80 kg for 8 reps → 80 × 36 / 29 = 99.3 kg
3. Lombardi Formula
The Lombardi formula uses a power function and is accurate for moderate rep ranges:
1RM = Weight × Reps^0.10
Example: 80 kg for 8 reps → 80 × 8^0.10 = 97.4 kg
Which formula should you use?
Use the Epley formula for 1-6 rep sets – it is the most common in powerlifting programs. Use Brzycki for 7-12 rep sets. Use Lombardi when you want a middle-ground estimate.
How GymPlateCalc helps
Our barbell calculator includes a built-in 1RM estimator. Enter the weight and reps from any working set and get your estimated max instantly. No manual math required.