360mm vs 420mm AIO: Extreme Cooling Compared

What 360mm and 420mm radiators are

All-in-one liquid coolers are named after the length of their radiator. A 360mm AIO has a 360mm radiator that mounts three 120mm fans, the format you will see called a triple-fan radiator. A 420mm AIO has a 420mm radiator that mounts three 140mm fans, which makes it the largest of the common AIO sizes for a desktop case.

Both are the top-end sizes when you choose liquid cooling for a desktop gaming PC. If you are comparing a tower air cooler against an AIO, the Air Cooling vs AIO for Gaming PCs article covers where each fits, and the CPU cooler guide lists liquid and air options by stated specifications.

Radiator surface area compared

The surface area of the radiator is the part the fans move air across. The 420mm radiator is the longer of the two, and the extra length adds surface area across the whole width of the radiator. That surface area is the dimension a build looks for when the processor has a high core count, because the radiator is the part of the loop that the case has to accommodate.

High-end desktop processors are the class you pair with a large radiator. The Intel Core Ultra series page lists processors with up to 16 cores and turbo frequencies up to 5 GHz, and the GeForce RTX 50 series page lists the graphics cards that sit in the same build, from the RTX 5060 through the RTX 5090. Processor naming separates desktop and mobile parts, with suffixes such as K and F marking desktop SKUs. The cooling solution article explains how a radiator fits into a full build.

Fan options: 120mm versus 140mm

The two radiator sizes use different fan sizes. The 360mm radiator takes three 120mm fans, and the 420mm radiator takes three 140mm fans. The 120mm fan is the most common case fan size, so a 360mm build can match its radiator fans with the rest of the case. The 140mm fan is a larger size, less common across case designs, and a 420mm build needs the case to support 140mm fans at the radiator mount.

The fan spacing on the radiator also differs. The mounting holes for 140mm fans sit wider apart than the holes for 120mm fans, so the radiator frame of a 420mm AIO is built for the larger fan, not just a longer version of the 360mm frame. The 120mm vs 140mm Case Fans article explains the difference in fan sizes.

Case compatibility for a 420mm radiator

The 420mm radiator is long, and that length is the first thing to match to the case. Most mid-tower cases mount a 360mm radiator at the top or the front, and the tower layout is built around that length. A 420mm radiator needs a case with a mounting point that spans 140mm fan spacing, which most full-tower cases provide. The Mid Tower vs Full Tower Case for Gaming article compares the two case classes.

When you choose a case for a large radiator, the front mount is the usual spot for a 420mm radiator, and the case has to leave room for the radiator and its fan stack behind the front panel. The Radiator Front vs Top Mount article covers the mounting positions, and the case size guide explains which tower dimensions matter.

Which size suits your play

The choice between a 360mm and a 420mm AIO is driven by the processor you want and the case you want around it. If the build runs a high-core-count desktop processor, a large radiator is the natural pairing, and the 420mm format is the largest surface you can fit when the case allows it. If you play at a high refresh rate on a 1440p or 4K display, or keep a large game library with a stream open at the same time, the processor is doing more work. NVIDIA's broadcasting page describes how the graphics card's encoder carries the stream so the processor can focus on the game. The streaming PC article covers the parts that support a game and a stream together.

For a desktop gaming PC on a standard desk, the 360mm format is the size that fits most cases and most layouts. The 420mm format is the size to choose when the case is a full tower and the build is centered on the largest possible radiator. The 360mm AIO guide lists current 360mm options by stated specifications.

Radiator placement in a desktop build

Radiator placement affects the rest of the build. A top-mounted radiator sits above the motherboard, and the fan thickness has to leave room for the memory sticks and the CPU power cables. A front-mounted radiator moves into the area that case fans usually occupy, which changes how the air moves through the tower. The case size article and the cooling solution article both place the radiator in the context of the whole build.

The same idea applies to a prebuilt gaming PC. A prebuilt with a large liquid cooler uses the 360mm format because the mid-tower cases in prebuilt lineups support that mount. A 420mm radiator is a custom-build choice, because it forces the case choice to a full tower. The prebuilt gaming PC guide explains what to check when a prebuilt lists its cooling setup.

What to pick for your play

Questions

Can a 420mm AIO fit in a mid-tower case?

Usually not. Most mid-tower cases are designed around a 360mm radiator mount at the top or front. A 420mm radiator needs a case with mounting points for three 140mm fans, which is the layout a full tower provides.

Which fans come with each radiator size?

A 360mm radiator uses three 120mm fans, and a 420mm radiator uses three 140mm fans. The fan spacing on the radiator frame is set for each size, so the fans are not interchangeable between the two radiators.

Does a 420mm radiator pair only with a full tower?

A 420mm radiator is long and needs the depth and the fan mount spacing of a full tower. If the case only lists a 360mm mount, the 420mm radiator will not fit.

Is a 420mm AIO worth choosing over a 360mm AIO?

The 420mm format offers more radiator surface area, which is the dimension that pairs with a high-core-count processor. The trade-off is the case requirement, because the larger radiator narrows the case choice to full towers. For most desktop gaming builds, the 360mm format fits a wider range of cases.

Which AIO size is common in a prebuilt gaming PC?

Prebuilt gaming PCs with a large liquid cooler typically use the 360mm format, because it fits the mid-tower cases that make up most prebuilt lineups. The 420mm format appears in full-tower builds where the case is chosen around the radiator. The prebuilt gaming PC guide explains what to check on a prebuilt's setup.