PSU measurements

Most desktop PCs use the ATX (PS2) standard, which is why replacing a failed unit is usually straightforward. Compact, branded and rack-mounted systems are where things get specific — a slim desktop, a Mini-ITX build and a 1U server enclosure can each demand a completely different shape, even when the connectors inside are identical.

• Measure width, height and depth in millimetres — not inches.
• Check the label on the side of your existing PSU; the form factor is often printed there.
• Confirm the screw hole positions line up, not just the overall footprint.
• Note where the power inlet and switch sit — some variants share dimensions but mount the socket on a different face.

ATX, SFX, TFX and 1U Flex are the four you'll meet most often — everything else below is a variant built for a specific case design.

The footprints found in the vast majority of home, office and gaming desktop cases.

ATX (PS2) 150 × 85 × 140 mm The industry-standard footprint used by most mid-tower and full-tower cases since the late 1990s. Widely interchangeable across brands. Best for: home & office towers, gaming PCs, general workstations.

PS3 150 × 85 × 100 mm A shortened ATX variant — same width and height, roughly 40mm shallower. Useful where a drive cage limits internal depth. Best for: compact towers with restricted depth.

Slim ATX 85 × 120 × 155 mm A flatter take on the ATX mounting pattern, built for low-profile desktop chassis rather than a full-height tower. Best for: branded slim-line desktops (HP, Dell).

Smaller footprints for slimline, Mini-ITX and space-constrained builds.

TFX 65 × 85 × 175 mm Thin Form Factor — narrow and long rather than square, built to slide into a slimline chassis an ATX unit couldn't fit inside. Best for: slimline desktops, SFF and HTPC cases.	SFX 125 × 76 × 100 mm Small Form Factor — roughly two-thirds the footprint of ATX, still capable of respectable wattages. Default choice for Mini-ITX. Best for: Mini-ITX builds, compact gaming PCs.	SFX Short 63 × 100 × 125 mm An SFX variant with the power inlet on the short side rather than the rear panel, for cases needing the socket to face another direction. Best for: Mini-ITX cases with a side- or top-mounted bay.
CFX 85 × 150 × 95 mm A less common footprint used by a handful of compact branded desktop machines — avoids paying a premium for an OEM-only part. Best for: select compact desktop models.

Built for rack-mounted, industrial and network-storage enclosures with strict height limits.

1U / 1U Flex 80 × 40 × 150 mm A very low-profile unit built to fit inside a single rack unit of height. Compact enough for POS terminals too. Best for: 1U rack servers, POS/EPOS systems.

1U 100mm 40 × 100 × 190 mm A taller, narrower 1U variant built for the deep, narrow bays typically found in NAS enclosures. Best for: 1U rack servers, NAS units.

2U PSU 70 × 100 × 220 mm Built for 2U industrial rack enclosures — more usable depth than 1U, while respecting a tight height allowance. Best for: 2U racks, networking & industrial gear.

All eleven form factors side by side. Dimensions are Width × Height × Depth in millimetres.

Replacing a failed unit? Three checks are usually enough to identify the correct form factor before you order.

Once the case fits, the next check is connectors. Our full PSU Connectors guide covers pin counts, voltages, wire colours and pinout diagrams for every connector type — from the everyday (ATX, SATA, Molex) to proprietary NAS connectors from Synology, QNAP and others.