Power Supply Unit PSU Form Factors and Dimensions
Choosing the right Power Supply Unit (PSU) form factor is critical for PC compatibility, cable clearance, and thermal airflow. Below is a comprehensive guide to standard power supply form factors, dimensions, and installation requirements.
Form Factor Quick Reference Table
Form Factor | Width | Height | Depth (Length) | Typical Fan Size | Common Applications |
|---|---|---|---|---|---|
Standard ATX | 150 mm | 86 mm | 140 mm – 160 mm (up to 200 mm+) | 120 mm / 140 mm | Mid-tower & full-tower desktop PCs |
SFX | 125 mm | 63.5 mm | 100 mm | 80 mm / 92 mm | Small Form Factor (SFF) Mini-ITX cases |
SFX-L | 125 mm | 63.5 mm | 130 mm | 120 mm | SFF cases needing high wattage/quieter fans |
Flex ATX | 81.5 mm | 40.5 mm | 150 mm (varies) | 40 mm | Ultra-compact SFF (under 10L), 1U rackmounts |
TFX | 85 mm | 65 mm | 175 mm | 80 mm | Low-profile desktop cases, OEM office PCs |
Frequently Asked Questions
1. What is ATX, and why does its length vary?
ATX (Advanced Technology eXtended) is the standard power supply specification used in most desktop enclosures.
- Fixed Dimensions: The width (150 mm) and height (86 mm) are strictly standardized to ensure mounting screw holes and rear cutout alignment across cases.
- Variable Length: The standard depth is 140 mm to 160 mm, but high-wattage units (1000W+) can extend to 180 mm – 220 mm to accommodate larger internal transformers and capacitor arrays.
- Compatibility Tip: Always measure the distance between the PSU shroud and drive bays in your PC chassis. A 180 mm unit will fit ATX mounting brackets, but it can block modular cable plugin clearances in compact Mid-Tower cases.
2. What is SFX, and how does it differ from SFX-L?
Both standards are engineered for Small Form Factor (SFF) builds, but they differ in depth:
- SFX Standard: Measures 125 x 63.5 x 100 mm. It features a compact 80 mm or 92 mm fan, leaving maximum room for cable routing inside dense mini-ITX cases.
- SFX-L (SFX Extended): Measures 125 x 63.5 x 130 mm (30 mm longer than SFX). This added depth allows manufacturer placement of a full-sized 120 mm fan, providing quieter operation and better cooling under heavy loads.
- Compatibility Tip: Many SFF chassis state "SFX support," but an SFX-L unit might collide with dedicated graphics card mounts or front-panel cable bundles due to the extra 30 mm depth.
3. What is Flex ATX?
Flex ATX is an ultra-slender power supply specification (81.5 x 40.5 x 150 mm) originally designed for 1U server racks and POS terminals. It has become popular in custom mini-ITX chassis under 10 liters (e.g., K39, Velka 3).
- Cooling & Noise: Flex ATX units use high-RPM 40 mm intake fans. Because small fans must spin faster to move sufficient air, stock Flex ATX power supplies can produce higher noise levels under load compared to SFX or ATX units.
4. Can I install an SFX power supply into a standard ATX case slot?
Yes. Most retail SFX power supplies ship with an SFX-to-ATX mounting adapter plate.
- The plate bolts to the smaller SFX housing and aligns with the standard 4-hole mounting pattern on standard ATX chassis.
- Cable Length Warning: Native SFX power supplies include shorter cables optimized for Small Form Factor cases (typically ~300mm for 24-pin EPS/ATX). If installed in a Mid-Tower or Full-Tower ATX case, these cables may not reach the motherboard header or CPU power socket without custom cable extensions.
5. What are TFX power supplies, and where are they used?
TFX (Thin Form Factor) units measure 85 x 65 x 175 mm. They are long and narrow, making them common in slimline office desktop PCs (e.g., Dell OptiPlex, HP Slim desktops) and low-profile media center cases. They are not interchangeable with ATX or SFX mounting mounts without custom modification.
6. Do modular PSU cables work across different form factors and brands?
No. Pinouts on the PSU side are not standardized.
Even if a modular cable physically plugs into a modular connector on a different power supply, the internal pin routing can differ significantly between manufacturers (or even different series within the same brand). Using mismatched modular cables can send incorrect voltage to components, resulting in hardware damage. Always use cables certified specifically for your exact PSU model.
Updated on: 03/09/2026
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