An AIO liquid cooler's radiator thickness spec looks like the number that decides whether it fits under your case's roof, and it isn't. The number that actually matters is radiator thickness plus fan thickness combined, and almost nobody publishes that sum anywhere near the spec sheet.
Two Numbers Get Confused for One
Manufacturers publish radiator thickness on its own, typically 27mm to 30mm for most 360mm and 280mm units, occasionally 38mm on thicker high-performance radiators. That number describes the radiator core alone, with no fans attached. The moment you bolt fans to it, which is how every AIO actually gets installed, the real stack height climbs well past the published figure.
A 38mm radiator with a pair of 25mm fans mounted flush against it needs roughly 63mm of clearance, not 38mm. Case manufacturers publish roof and front clearance in exactly that combined measure, radiator plus fans, so a buyer comparing the cooler's radiator-only spec against the case's stack clearance spec is comparing two different things and will consistently underestimate how much room the cooler actually needs.
Why the Mismatch Persists
Radiator thickness is the more flattering number for a cooler listing, since thinner sounds like a more universally compatible product. Publishing the combined stack height would require the manufacturer to commit to a specific fan choice, and many AIOs ship in configurations where the bundled fans vary or where buyers swap in their own. So the ambiguity gets pushed onto the buyer instead of resolved at the spec sheet.
This matters most for cases with a front radiator mount close to the front panel or a top mount with limited clearance to the motherboard's VRM heatsinks. A thin-looking radiator on paper can still be a tight fit once real fans are attached, especially in push-pull configurations that stack two fans on one side.
What to Actually Check Before Buying
Add the radiator's published thickness to your fans' thickness rather than trusting the radiator number alone, and check that combined figure against your case's published stack clearance, not just its radiator size support. If you're planning push-pull fans on both sides of the radiator, double the fan thickness in that calculation. And when a case manufacturer doesn't publish a stack clearance figure at all, treat the radiator's own maximum supported thickness as the more conservative number to plan around.
Winner
Radiator thickness alone is not a reliable compatibility number. Always calculate radiator plus fan thickness together, and check that combined figure against your case's actual stack clearance before assuming a cooler will fit.
Pros and Cons
Radiator-only thickness specs: Simple and consistent across most product listings, but they systematically understate real-world clearance needs once fans are attached.
Combined stack height figures: Rarely published, but the only number that reliably predicts whether an AIO will actually fit a specific case and mounting position.
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