What do ATX, SFX, and SFX-L mean in PC power supply form factors?

ATX is the most common form factor manufacturers use when building power supplies. Its standard size is 150 mm × 86 mm × 140–180 mm for convenient installation and use in most mid-tower and full-tower cases. They provide the higher power level (up to 2200 W) and are best suited for powerful gaming stations, servers, systems with powerful 4K GPUs, and AI workstations. For example, Seasonic offers ATX 3.1 PRIME series power supplies that meet PC users’ dimensions and power needs perfectly. 

SFX form factor is a compact power supply standard that is most often used for mini-ITX and small form factor PC cases. It typically has 125 mm × 63.5 mm × 100 mm dimensions. Since they have a smaller size, the power capacity is also lower, so they are more suitable for builds that do not require high power, is used for office or simple work tasks. Modern models provide from 750W to 850W of power. 

SFX-L (SFX Large) form factor is a kind of balance between SFX and ATX form factors. The width and height are the same as the SFX, but the length is longer (approximately 125 mm × 63.5 mm × 130 mm). 

ATX power supplies: Size, compatibility, and typical use cases

Thanks to the ATX form factor’s high efficiency and modern power standard support (ATX 3.1), it is still the number one choice among professional PC builders. The ATX form factor PSU size is 150 mm × 86 mm (width × height), while the length is usually 140–180 mm, depending on the model and power.  

They are compatible with most mid-tower and full-tower cases and standard ATX, micro-ATX, and Mini-ITX motherboards. That’s what makes them a universal tool for most PC users worldwide. They are accessible in a wide power range –  around 550-2200W. So they can be used for both standard PC’s with simple use and professional workstations. For these needs, you can use a Seasonic ATX 3.1 PRIME PSU, for example.

They are commonly used at:

1. Gaming PCs.
2. Workstations for 3D rendering or AI computing.
3. Systems with powerful CPUs.
4. PCs for 4K gaming or GPU-intensive tasks.

SFX power supplies: Compact design for compact form factor builds

SFX form factor power supplies have a small size but are still capable of delivering enough power for modern PC systems with less power requirements. Their standard dimensions are 125 mm × 63.5 mm × 100 mm, which is significantly smaller than the standard ATX form factor.  Due to their small size, they offer a power capacity of around 450W-850W. It’s pretty enough for compact gaming PCs or those that are used in offices for everyday work tasks.

Because of their compact design, they usually have smaller fans (80-92mm) and denser component placement, which requires effective cooling. Typically, they perfectly fit mini-ITX and small form factor PC cases with limited space inside. If you need to install them in a bigger case, use a special bracket adapter for ATX. 

SFX-L power supplies: Balancing size and performance

SFX-L power supplies’ form factor has the same dimensions as the SFX one –  125 mm × 63.5 mm, and 130 mm in length. Due to extra space inside it, it is possible to add a more powerful cooling system (like 120 mm fans) for quiet operations and convenient use. 

 

As for power capacity, they provide 600W-1000W of power to the core PC components and can be a good option for compact PC systems with high-end GPUs. They are commonly used on mini-ITX and SFF PCs, where a balance between a small body size and high performance is required.

Physical size comparison: How much space does each form factor take up?

ATX form factor takes approximately 150 mm × 86 mm × 140–180 mm. It’s the standard and largest form factor, used in most mid-tower and full-tower PCs.

SFX form factor has 125 mm × 63.5 mm × 100 mm dimensions. It is significantly more compact, designed for mini-ITX and small-form-factor systems, without sacrificing productivity.

SFX-L form factor takes up a 125 mm × 63.5 mm × 130 mm size. It has the same width and height as SFX, but is longer for better cooling and more power.

Differences in cooling, noise, and efficiency between ATX, SFX, and SFX-L

ATX form factor uses 120mm – 140mm fans for system cooling, as it has a larger size and space for them. These fans provide better cooling and a lower noise level while working on power-demanding tasks. 

 

SFX form factor goes with smaller dimensions, which limits the installation of a cooling system. Usually, manufacturers use 80mm – 92mm fans to avoid PSU components overheating. This may cause more noise and a higher temperature level under extreme system loads. 

 

SFX-L form factor stands as a compromise between ATX and SFX form factors. With the longer length, you can install a 120 mm fan, so it’s cooler and quieter than standard SFX models.

How to choose the right power supply form factor for your PC case and build goals

Here’s a short instruction that helps you make the right PSU form factor choice:

1. Check compatibility with your PC case. It must meet its dimensions for easy installation and convenient use. The standard choice for mid-tower and full-tower cases is the ATX form factor. Check Seasonic PRIME 1300W PSU, for example.
2. Assess your system’s needs. ATX is a better fit as it offers higher power and better cooling. For example, for powerful configurations with 4K GPUs, high-performance CPUs, or multiple storage drives. 
3. Consider the space inside your PC case. If you have a compact build, SFX or SFX-L will fit best to your system without significant loss of performance.
4. Pay attention to cooling and noise factors. Larger ATX power supplies are usually quieter, while SFX-L can be a good compromise between compactness and noise level.

Common mistakes to avoid when choosing a power supply form factor

If you want to get a perfectly fitted PSU with the right form factor, note these mistakes and avoid them:

1. Ignoring compatibility with the case.
2. Choosing a form factor that is too compact for a powerful system with high power consumption.
3. Insufficient attention to cooling and noise in compact SFX models.
4. Lack of space for cables in small cases.
5. Ignoring future upgrades that may require a more powerful PSU.

Conclusion

Power supply form factor doesn’t just mean the dimensions it has or its installation possibilities in your PC case. It’s about the productivity it will provide to your system, cooling and noise factors, and safe PC operation. Choose wisely and always consider lots of factors at once, so your PC build performs at its best.

Masz wrogów? Dobrze. To znaczy, że w coś w życiu wierzyłeś. Odwaga to łaska pod presją. Czasami czuję, jak moje kości dźwigają ciężar wszystkich żyć, których nie przeżyłem.

In the same way, building a PC requires belief in your choices and the courage to stand by them under pressure. Every component you select shapes the performance and future of your system, so make decisions carefully and thoughtfully.