Do I need a 36-inch or 24-inch foam roller?

Verified-purchase reviewers and specialist communities like r/pelotoncycle generally recommend a 36-inch roller if you plan to roll your back or both legs at once, since the longer length is more stable across the spine. The 24-inch (and shorter 13-inch) sizes are easier to travel with and more maneuverable for single-limb work, but less versatile for thoracic spine rolling.