What is a PC form factor?

A form factor is a standardised specification defining the physical dimensions, mounting-hole pattern, I/O panel cut-out and power-connector layout of a motherboard. The same form factor lets you mix and match motherboards, cases, power supplies and coolers from any brand. ATX, the dominant standard since 1995, measures 305 x 244 mm and is the assumed default if no specific form factor is mentioned.

What are the main motherboard form factors?

In 2026 there are five mainstream motherboard sizes. E-ATX (305 x 330 mm) is the workstation and high-end-desktop king with up to eight DIMM slots and seven expansion slots. ATX (305 x 244 mm) is the standard for full gaming builds, four DIMMs and seven slots. Micro ATX (244 x 244 mm) keeps four DIMMs but drops to four slots, fitting compact cases. Mini ITX (170 x 170 mm) is the smallest practical builder size — two DIMMs, one expansion slot. SSI-EEB (305 x 330 mm) is the dual-socket server standard for Xeon and EPYC workstations.

Does my case need to match my motherboard size?

Your case must support your motherboard form factor — but bigger cases fit smaller boards. A full-tower ATX case accepts Mini ITX, Micro ATX and ATX boards. A Micro ATX case usually accepts Micro ATX and Mini ITX. A dedicated Mini ITX case only fits Mini ITX boards. The case spec sheet lists supported sizes. Buying a too-small case is the single most common build mistake — check before buying.

What is an ATX power supply versus SFX?

Standard ATX PSU measures 150 x 86 x 140 mm and fits any standard full-size case. SFX measures 125 x 63.5 x 100 mm — designed for Mini ITX small-form-factor (SFF) cases where space is tight. SFX-L (125 x 63.5 x 130 mm) is the in-between option with quieter larger fans. Pricing in SA: SFX units cost roughly 30-50% more than ATX equivalents for the same wattage because of lower production volumes.

Why do Mini ITX builds cost more in South Africa?

Three reasons. First, the motherboards themselves use denser PCB layouts and cost 20-40% more than ATX equivalents at the same chipset tier. Second, SFX power supplies cost more than ATX. Third, low-profile cooling (NH-L9, NH-L12, AIO with 120mm radiators) commands a premium because of small-volume production. A R30,000 mid-range ATX gaming PC typically lands R34,000-R37,000 in equivalent Mini ITX form.

Which form factor is right for me?

ATX for 90% of builds — best value per watt, best cooling headroom, widest case selection in SA. Micro ATX if you want a smaller desk footprint without paying ITX premiums. Mini ITX only if portability or aesthetic minimalism is the primary driver — LAN party builds, lounge HTPCs, RGB showcase builds. E-ATX or SSI-EEB only for Threadripper or Xeon-W workstations needing eight DIMM slots.

What is the most popular form factor in SA?

ATX dominates SA gaming builds — roughly 65-70% of custom builds we ship from our Centurion warehouse. Micro ATX accounts for 18-22%. Mini ITX is 8-12% (and growing among premium aesthetic builders). E-ATX and SSI-EEB combined are under 3%, almost entirely workstation and content-creator builds.

How has the form factor landscape evolved?

BTX and DTX attempted to displace ATX in the mid-2000s and failed. Since 2010 the trend has been miniaturisation — ITX going mainstream, SFX PSUs improving in quality and dropping in price (slightly). The 2026 reality: ATX remains the centre of gravity, ITX has matured into a legitimate premium-build option, and the BTX-style attempts to reshape PC layout entirely have all failed. Form factor stability is what makes PC building viable two decades after the iMac killed beige-box compatibility.

Glossary · Form Factor

What is a form factor? — PC sizes, drawn to scale.

Five standardised motherboard sizes account for 99% of desktop PCs sold in 2026. Pick the right one and every part fits the next part. Pick wrong and you'll fight your case for the lifetime of the build.

8 min read
Updated June 2026
Reviewed by Evetech Hardware Team

In this glossary entry, you'll see every mainstream board form factor drawn to scale, the exact case and PSU each one needs, and why Mini ITX builds cost 15% more in SA.

ATX mm: 305×244
Mini ITX mm: 170×170
cover 99%: 5 sizes

What "form factor" actually means

A motherboard form factor is a published specification — first standardised by Intel in 1995 as ATX (Advanced Technology Extended) — that defines four things: the physical dimensions of the PCB, the mounting hole pattern for screwing it to a case, the I/O panel cut-out at the back, and the power-connector layout for the PSU.

The standard exists for one purpose: interoperability. An ATX motherboard from ASUS bought in 2026 mounts into an ATX case from Phanteks bought in 2018 using mounting holes specified in a 1995 document. The cooler fits because the AM5 or LGA1851 socket sits at the standardised position. Your PSU connects because the 24-pin and CPU EPS connectors are where every PSU expects them.

The five mainstream sizes

Form factor	Dimensions (W × D)	Where it's used
E-ATX	305 × 330 mm	HEDT, Threadripper, content workstations
SSI-EEB	305 × 330 mm	Dual-socket Xeon, EPYC server boards
ATX	305 × 244 mm	Standard gaming, mainstream desktops
Micro ATX (mATX)	244 × 244 mm	Compact mainstream, office, budget gaming
Mini ITX (ITX)	170 × 170 mm	SFF builds, lounge HTPCs, LAN portables

E-ATX and SSI-EEB look identical on paper but are not interchangeable in every case — the mounting hole spacing differs and SSI-EEB boards typically have an extra row of mount points. Always check the case spec sheet calls out the specific size you're buying.

Case-size dependency — bigger fits smaller

A case is rated for the largest motherboard it accepts. Larger cases accept smaller boards without modification — the smaller board uses the matching subset of mount points.

Case class	Accepts	Typical example
Full tower	E-ATX, ATX, mATX, ITX	Phanteks Enthoo Pro 2, Lian Li PC-O11D XL
Mid tower	ATX, mATX, ITX	Corsair 4000D, NZXT H7, Fractal North
Micro tower	mATX, ITX	Cooler Master MasterBox NR400
Mini tower / ITX case	ITX only	NZXT H1, Fractal Terra, Lian Li A4-H2O
HTPC / console-style	ITX only (usually)	Fractal Ridge, Cooler Master NR200P

Expansion slots — what each size gives you

Smaller boards mean fewer PCIe slots. For most modern builds (single GPU + maybe a sound card or capture card), this matters less than it did 15 years ago. But if you're planning multi-GPU AI workloads, 10G networking PCIe cards, or expansion storage controllers — slot count is decisive.

Form factor	PCIe slots	DIMM slots
E-ATX	7 (often 4 full-length)	4 or 8
SSI-EEB	7 (server-spec spacing)	8 or 16
ATX	7 (3-4 full-length usually)	4
Micro ATX	4 (2-3 full-length)	4 (occasionally 2)
Mini ITX	1 (full-length only)	2

PSU form factors — ATX vs SFX vs SFX-L

PSUs have their own form factor spec, which must match what the case supports. Three sizes cover almost everything:

PSU type	Dimensions (W × H × D)	Where it fits
ATX (standard)	150 × 86 × 140 mm	Every full / mid / micro tower
ATX (long)	150 × 86 × 180 mm	1000W+ high-end units
SFX	125 × 63.5 × 100 mm	Mini ITX cases, some mATX SFF
SFX-L	125 × 63.5 × 130 mm	ITX cases with longer PSU bay, quieter fan
TFX	175 × 65 × 85 mm	Slim OEM cases (rare in retail)
Flex ATX	81.5 × 40.5 × 150 mm	Very narrow SFF cases (rare)

SFX-L is the SFF sweet spot in 2026 — only marginally larger than SFX but with a 120mm fan that runs noticeably quieter than the 92mm fan on standard SFX units. Corsair SF750L, Cooler Master V750 SFX-L and Silverstone SX1000R-PL all retail in SA.

Why Mini ITX builds cost more in SA

An ITX equivalent of a R30,000 mid-range ATX gaming build typically lands R34,000-R37,000. Three reasons:

Motherboard premium. ITX boards use denser PCB layouts (more layers, finer trace routing) and ship at lower production volumes. A B650 ATX board lands ~R3,800; a B650 ITX equivalent runs R5,400-R6,500.
PSU premium. SFX 750W gold lands R2,800-R3,500; equivalent ATX runs R1,900-R2,500. SFX-L is even more.
Cooling premium. Low-profile NH-L9, NH-L12, AsRock NSP, Cryorig C7 and slim 120mm AIOs all carry a small-volume premium. A standard 240mm AIO runs R2,200; a 240mm AIO designed for ITX with short tubes can be R3,000-R3,400.

The case itself isn't necessarily more expensive — but it constrains everything inside it.

Which form factor suits you

You are…	Pick	Why
Standard gaming build R20-50k	ATX	Best value, widest case selection, easiest cooling
Budget gaming under R20k	Micro ATX	Saves R500-R1000 vs ATX, fits smaller desk
Office workstation	Micro ATX	4 DIMMs, single GPU slot — everything you need
LAN-party portable	Mini ITX	Pack it in a backpack, plug in anywhere
Aesthetic showcase build	Mini ITX	Lian Li A4 / Fractal Terra wow factor
HTPC / lounge PC	Mini ITX	Fits AV cabinet, looks like a console
Content creator / 3D / video	E-ATX	Threadripper, more PCIe lanes, more DIMMs
Dorm / student desk	Micro ATX	Compact, affordable, dual-monitor ready
Multi-GPU AI / Render	E-ATX or SSI-EEB	Multiple full-length slots with spacing

The evolution — how we got here

Form factor stability is the unsung hero of PC building. The same ATX spec that Intel published in 1995 still governs the case you're considering today. Brief timeline:

1984 — IBM PC AT (12 × 13 inches), the ATX predecessor. Big, beige, terrible airflow.
1995 — Intel publishes ATX spec. Moves CPU and RAM next to PSU for better cooling.
1997 — Micro ATX published, drops two expansion slots for smaller footprint.
2001 — VIA publishes Mini ITX spec, originally for embedded and industrial.
2003 — BTX spec released by Intel, attempts to displace ATX. Fails by 2006.
2010-2015 — Mini ITX goes mainstream as gaming SFF cases reach maturity.
2024-2026 — ATX 12V O.2 (12VHPWR / 12V-2x6) connector standardised for high-wattage GPUs. PSU shape unchanged.

The form factor hasn't changed because every attempt to change it has failed. BTX, DTX and proprietary OEM specs (looking at you, Dell and HP "desktop minitower") all lost to ATX. The reason: ATX is good enough, and the ecosystem of cases, coolers, PSUs and boards built around it represents thirty years of compounding interoperability.

Key takeaways

Form factor = standardised motherboard dimensions, mount holes and connector positions.
Five mainstream sizes: E-ATX, SSI-EEB, ATX, Micro ATX, Mini ITX — cover 99% of builds.
Bigger cases fit smaller boards — always check the case spec for "Motherboard support".
PSU form factor matters too: ATX standard, SFX/SFX-L for ITX builds.
ATX for 90% of buyers — Mini ITX runs 15-20% more in SA due to denser parts.

Frequently asked questions

What is a PC form factor?
Standardised specification defining motherboard dimensions, mounting holes, I/O cut-out and power connector layout. Lets you mix and match cases, PSUs and boards across brands.
What are the main motherboard form factors?
E-ATX (305×330 mm), ATX (305×244), Micro ATX (244×244), Mini ITX (170×170), SSI-EEB (server dual-socket).
Does my case need to match my motherboard size?
Case must support your board size or larger. ITX boards fit any ATX or mATX case. Check case spec sheet before ordering.
What is an ATX power supply versus SFX?
ATX (150×86×140 mm) fits standard cases. SFX (125×63.5×100 mm) for ITX SFF. SFX-L slightly bigger with quieter fan.
Why do Mini ITX builds cost more in South Africa?
Denser PCB motherboards, SFX PSU premium, low-profile cooling premium. Typical 15-20% surcharge versus equivalent ATX build.
Which form factor is right for me?
ATX for 90% of builds. mATX for compact mainstream. Mini ITX for portability or aesthetic. E-ATX for Threadripper / Xeon-W workstations.
What is the most popular form factor in SA?
ATX at 65-70% of custom builds we ship. Micro ATX 18-22%. Mini ITX 8-12% and growing. E-ATX / SSI-EEB combined under 3%.
How has the form factor landscape evolved?
ATX has dominated since 1995. BTX and DTX failed to displace it. Trend since 2010: miniaturisation, ITX going mainstream. 2026: ATX still the centre.