Radiator sizing comes down to two questions: how much heat you need to dissipate, and how much room your case actually has. A single CPU loop is comfortable with a 240mm or 280mm radiator in most mid-tower cases. Add a GPU to the loop and you will want to step up to a 360mm, or consider a secondary radiator if your case supports it.

Thickness matters as much as length. A thicker radiator paired with lower RPM fans is often quieter than a thin radiator running high RPM fans to hit the same temperatures, so do not assume a bigger radiator automatically means a louder build.

Always measure your case's radiator mounting points before ordering, including clearance for fittings and tubing. A radiator that technically fits the mounting holes can still crowd out fan headers or motherboard components.