Measure PC Case for SFX Power Supply Fit

This guide shows you how to measure your PC case to confirm whether an SFX (Small Form Factor) power supply will fit. You’ll take a few key dimensions—mounting width, depth, and clearance—and compare them against the standard SFX size. By the end, you’ll know exactly what to check before buying, avoiding a return or a build that won’t close.

What You’ll Need

• Tape measure or ruler (metric or imperial, but be consistent)
• Notepad and pen (or a notes app) to record measurements
• Access to the inside of your PC case (remove the side panels)
• Screwdriver (usually Phillips) to remove panels if needed
• Flashlight or good lighting to see inside the case

Step-by-Step

1. Power down and unplug the PC. Safety first—turn off the PSU switch and disconnect the power cord. Also ground yourself by touching a metal part of the case to avoid static damage.
2. Remove the side panels. Most cases have thumbscrews or standard screws at the rear. Take off both panels so you can access the PSU mounting area from both sides.
3. Locate the PSU mounting bracket or bay. This is usually at the top or bottom rear of the case. It may be a removable metal bracket, a set of screw holes on the back panel, or a dedicated shroud. If there’s a removable bracket, take it out to measure it more easily.
4. Measure the mounting width. The standard SFX power supply is 125 mm wide (4.92 inches). Measure the distance between the two sets of screw holes on the bracket or the internal width of the bay. This must be at least 125 mm (plus a little slack for the screw holes to align). If it’s less, an SFX unit won’t mount.
5. Measure the mounting depth. SFX units are 100 mm deep (3.94 inches) from front to back. Measure the distance from the back panel (where the plug goes) to the front of the bay or any obstruction (like a drive cage or cable shroud). You need at least 100 mm, plus a few millimeters for cables and airflow. Note: SFX-L units are 130 mm deep, so if you’re considering one, measure for that too.
6. Check the height clearance. SFX is 63.5 mm tall (2.5 inches). Measure from the bottom of the bay (or the top, depending on orientation) to any component above or below—like a graphics card, CPU cooler, or top-mounted radiator. Ensure there’s at least 63.5 mm of clear space.
7. Verify the screw hole pattern. SFX uses four screws, typically spaced 71.5 mm apart horizontally and 51.5 mm vertically (the same pattern as ATX, but the overall size is smaller). Compare your case’s holes to this pattern. If the holes are too far apart, you may need an adapter bracket (many cases include one for SFX in an ATX bay).
8. Check the rear opening. The cutout in the back panel for the power cord and switch must match the SFX layout. Measure the opening—it should be roughly 62 mm wide by 30 mm tall. If it’s larger (ATX-sized), you’ll need an adapter plate to cover the gap.
9. Consider cable clearance. Even if the PSU itself fits, the cables need room to bend and route. Measure from the PSU mounting position to the nearest obstruction (e.g., drive cage, shroud) in the direction cables will exit. Add at least 20–30 mm for cable management.
10. Record all measurements. Write down each dimension and compare them to the SFX spec: 125 mm wide, 100 mm deep, 63.5 mm tall. If all your measurements are equal to or greater than these, an SFX PSU will fit. If any are short, it won’t—or you’ll need a different size (like Flex ATX) or a case modification.

Common Mistakes

• Measuring the outside of the case instead of the inside. The internal bay is what matters; the outer shell can be misleading.
• Forgetting to account for the PSU’s own connectors. The modular ports on the back add a few millimeters to the depth. Always add 5–10 mm to your depth measurement.
• Ignoring the screw hole pattern. Even if the space fits, the holes must align. Measure the distance between holes, not just the overall space.
• Assuming SFX-L will fit just because SFX does. SFX-L is 130 mm deep—30 mm longer. Always check the specific model’s dimensions.
• Not checking the orientation. Some cases mount the PSU in a vertical orientation; make sure you measure the correct axis for width and height.

Tips

• Use a digital caliper for the most accurate measurements, especially for screw hole spacing.
• If your case has a removable PSU bracket, measure it on a flat table—it’s much easier than measuring inside the case.
• Check your case manufacturer’s website for a spec sheet. Often they list supported PSU sizes, which can save you the trouble.
• When in doubt, buy a slightly smaller PSU (like an SFX instead of SFX-L) to leave more room for cables.
• Take photos of your measurements so you can refer back to them when shopping.

Troubleshooting

If the PSU doesn’t fit:

• Check for an adapter bracket. Many cases include a metal plate that converts an ATX bay to SFX. If you have one, install it and re-measure the effective space.
• Remove obstructions. If a drive cage or shroud is in the way, see if it’s removable. Many modern cases have modular drive cages that can be relocated or taken out entirely.
• Consider a different form factor. If SFX is too tight, look at Flex ATX (81.5 mm × 40.5 mm × 150 mm) or TFX (85 mm × 65 mm × 175 mm), but check if your case has the right mounting holes.
• Use a shorter PSU. Some SFX units are slightly under 100 mm deep; check the exact specs of the model you want.
• If the screw holes don’t align but the size fits, you can carefully drill new holes (only if you’re comfortable and the metal is thick enough), but this voids warranty and risks damaging the case.
• If the rear opening is too small, you may need to file it open slightly—but this is risky and should be done slowly with a metal file, ensuring no debris falls inside.

Frequently Asked Questions

Can I use an SFX PSU in an ATX case?

Yes, but you’ll need an adapter bracket. Most ATX cases have mounting holes for both ATX and SFX, or you can buy a metal plate that covers the larger ATX opening.

What’s the difference between SFX and SFX-L?

SFX-L is longer: 130 mm deep versus 100 mm for standard SFX. Both share the same width (125 mm) and height (63.5 mm). The extra length accommodates a larger fan or higher wattage.

How much clearance do I need around the PSU?

At least 5–10 mm on each side for airflow and to avoid vibration. More is better, especially for the fan intake—leave at least 10 mm between the fan and the case wall.

Can I measure the case without removing the motherboard?

Usually yes, as the PSU bay is separate. If the bay is behind the motherboard tray, you may need to remove the motherboard to access it, but that’s rare.

What if my case has a bottom-mounted PSU shroud?

Measure the space inside the shroud. SFX units fit easily in most shrouds, but check the depth—some shrouds are short and may not accommodate the cables.

Do all SFX power supplies have the same screw hole pattern?

Yes, the standard is 71.5 mm × 51.5 mm spacing. If your case has holes that match this, any SFX PSU will mount.

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