# Mini-ITX builds: where the money goes and what actually limits you

> Case volume, GPU length, SFX power, cooler height and PCIe risers — the five constraints that decide whether an ITX build is quiet, fast or a compromise.

**Tested on**

- Build: 26300.9457
- Edition: Pro (26H2)
- Architecture: x64
- Evidence: E1
- Verified: 2026-10-29

## The short answer

Mini-ITX is not "a small PC". It is a **budget of five hard numbers**, and every case spends them differently:

| Constraint | What it limits | Typical ITX range |
|---|---|---|
| **Case volume** | everything else | 8–23 L |
| **GPU length** | the GPU you can buy | 170–330 mm |
| **Cooler height** | CPU cooling, therefore noise | 37–70 mm |
| **PSU format** | wattage and noise | SFX/SFX-L, 450–850 W |
| **Riser** | GPU orientation, PCIe generation | none, or 3.0/4.0 ribbon |

Pick the case **first**, then let it veto components. The reverse order — buying a GPU, then hunting a case — is how ITX builds turn into returns.

## The five numbers, in the order they bite

### 1. Case volume sets the class

| Class | Volume | What you get | What you give up |
|---|---|---|---|
| Console/A4 | 8–11 L | console-shaped, one GPU, one SSD | hot air recirculation, cable space |
| Classic ITX | 12–17 L | tower cooler or 240 mm AIO | GPU length |
| Mesh/sandwich | 15–20 L | big GPU + decent cooling | desk footprint |
| mATX-in-ITX case | 20–23 L | cheaper boards, more room | it is not really small |

Below ~10 L, cooling becomes the design problem, not the component choice.

### 2. GPU length and thickness

Three numbers, all must fit: **length**, **height** (from the PCIe slot), and **thickness** (2 vs 2.5 vs 3 slots).

A 330 mm card needs a case that states 330 mm *for that slot position*; many "supports 330 mm" claims assume a low-profile power connector. Check the vendor's clearance diagram, not the marketing line.

### 3. Cooler height

| Height | What fits |
|---|---|
| 37–45 mm | low-profile, noisy under load |
| 45–55 mm | mid low-profile, acceptable on 65 W |
| 55–70 mm | good tower coolers, 105–125 W class |
| 70 mm+ | only in 15 L+ cases or with an AIO |

A 240 mm AIO needs a case that lists radiator support **and** hose routing. In a 12 L case that usually means the GPU moves to a riser.

### 4. PSU: SFX, and transient spikes

SFX-L gives you a bigger fan (quieter) at the cost of ~10 mm. Wattage matters less than **transient response**: modern GPUs spike to 2× their rated power for milliseconds, and a small PSU with aggressive OCP shuts down.

See [PSU sizing](https://windows.homes/en/hardware/build/psu/) for the spike maths. For ITX, prefer 650 W+ SFX from a vendor whose cables are short and flexible — cable stiffness is a real build constraint at 10 L.

### 5. Risers change the PCIe generation

A PCIe 3.0 riser in a 4.0 slot either trains down (fine, slower) or fails to POST (common, confusing). If the board and GPU are 4.0+, buy a **4.0-rated** riser, and set the slot to Gen 3 in UEFI only as a diagnostic.

## What this means for Windows specifically

Nothing changes in the OS — but three things are worth knowing:

- **Windows 11 hardware floor is unchanged**: TPM 2.0, Secure Boot, supported CPU ([the OS/hardware matrix](https://windows.homes/en/hardware/buy/os-hardware-matrix/)). ITX boards ship these, but a **TPM header** must be populated on some AMD boards.
- **Thermals look different in a small case.** A 65 W CPU in 10 L can run hotter than a 125 W CPU in 40 L. Measure, do not assume — see [thermal measurement](https://windows.homes/en/hardware/diag/measurement-method/).
- **Firmware updates are riskier** because a power loss during flash in a cramped case with a marginal SFX PSU is a real scenario. Suspend BitLocker first ([drill](https://windows.homes/en/windows/hardening/bitlocker-recovery-drill/)).

> **Tip: The ITX rule that saves the most money**
>
> Choose the **GPU** and the **cooler** first as a pair, then buy the smallest case that fits both with 5 mm to spare. Cases are the cheapest part to change and the most expensive part to get wrong.

## A worked example

Target: 1440p gaming, quiet, under 20 L.

| Part | Choice | Why |
|---|---|---|
| Case | 17–18 L mesh, 330 mm GPU, 70 mm cooler | leaves room for a real cooler |
| GPU | 2.5-slot, ~300 mm | fits with the front panel on |
| Cooler | 65 mm tower or 240 mm AIO | 65 W–105 W class CPU |
| PSU | 750 W SFX, short cables | handles transient spikes |
| Board | ITX, TPM header or fTPM enabled | Windows 11 requirement |

## Costs people forget

- **Motherboard premium**: ITX boards cost more than mATX for fewer slots.
- **SFX PSU premium**: 20–40% over ATX for the same wattage.
- **Riser**: 30–60 for a 4.0 ribbon.
- **Cable customisation**: often the difference between "closes" and "bulges".
- **Time**: an ITX build takes 2–3× a mid-tower build.

## Related

- [Airflow and pressure](https://windows.homes/en/hardware/build/airflow/)
- [PSU sizing and transient spikes](https://windows.homes/en/hardware/build/psu/)
- [A mini PC or old laptop as a Proxmox host](https://windows.homes/en/hardware/homelab/mini-pc-host/)

## Lab boundary

E1. The constraints are physical and vendor-published; Windows requirements are Microsoft-documented. This lab has no ITX hardware, so no build was assembled or thermally measured.

## Sources

- [Microsoft Learn — Windows 11 processor requirements](https://learn.microsoft.com/en-us/windows-hardware/design/minimum/windows-processor-requirements)
- [Microsoft Learn — What is new in Windows 11](https://learn.microsoft.com/en-us/windows/whats-new/windows-11-overview)
- [Microsoft Learn — Bring up and firmware](https://learn.microsoft.com/en-us/windows-hardware/drivers/bringup/)

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Source: https://windows.homes/en/hardware/build/mini-itx/