One Rep Max Calculator

What Is a One Rep Max Calculator?

A one rep max (1RM) calculator uses a proven mathematical formula to estimate your maximum single-repetition strength based on submaximal performance. The tool takes two inputs — the weight lifted and the number of reps completed — and returns your estimated max using the Epley formula. It also generates a percentage chart showing weights at 50%, 60%, 70%, 80%, 85%, 90%, 95%, and 100% of your max, which is essential for following any percentage-based strength program.

How to Use the One Rep Max Calculator

1. Complete a working set: Perform a set of 3-10 reps with a challenging weight using strict form. The fewer reps (closer to 3-5), the more accurate the estimate.
2. Enter the weight: Type the weight you used in pounds or kilograms.
3. Enter the reps: Type the number of clean, full-range repetitions you completed.
4. Use the percentage chart: Read your estimated 1RM and use the percentage breakdown to set weights for your next training session.

Who Is This For?

• Intermediate and advanced lifters running structured programs like Wendler's 5/3/1, Juggernaut Method, or GZCL who need percentage-based training weights.
• Coaches and personal trainers who need to quickly estimate client maxes without putting them through risky maximal attempts.
• Anyone returning from a training break who wants to establish a new baseline without testing true maxes on day one.

Key Benefits

• 100% private — your data stays on your device.
• Epley formula — the most widely used and validated 1RM estimation method.
• Free, no login — use it between sets at the gym.
• Full percentage chart — instantly see training weights from 50% to 100%.

Common Use Cases

Starting a new program: Your new program requires training maxes. Enter your best recent set (e.g., 185 lbs for 6 reps) and use the estimated max to calculate all training weights for the cycle.

Post-injury baseline: After rehabbing a shoulder injury, do a cautious set of 8 at 135 lbs on bench. The calculator estimates your current max so you can program a safe return-to-training plan.

Comparing lifts: Your estimated squat max is 315 and your estimated deadlift max is 365. You can identify strength imbalances by comparing estimated maxes across movements.

Frequently Asked Questions