How to Use This Calculator

This tool uses the “Effective Reps Model” to estimate how many repetitions in your set are actually contributing to muscle hypertrophy.

• Total Reps: The total number of repetitions you performed in the set.
• RIR (Reps In Reserve): How many more reps could you have done with good form before reaching failure? (e.g., If you stopped but could have done 2 more, your RIR is 2).

The Math Behind Effective Reps

According to modern hypertrophy research, not all repetitions are created equal. In a standard set (performed with light to moderate weight), only the repetitions that recruit high-threshold motor units trigger significant growth.

These motor units are typically only recruited during the last 5 reps before muscular failure.

The Formula:
Effective Reps = 5 – RIR (Reps in Reserve)

If you perform a set of 12 reps but stop with 5 reps left in the tank (5 RIR), you have performed zero effective reps. You have accumulated fatigue (volume) without the growth stimulus.

Stop Calculating Manually

Doing this math for every single set in your workout is tedious. That is why we built Strive Gym Log.

Strive automatically calculates your effective reps for every exercise based on the RPE/RIR you log. It tracks this metric over time, allowing you to ensure you are consistently overloading your muscles, not just adding empty volume.