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Motherboard form factor guide
To increase general awareness of PC users on motherboard sizes and form factors, the following outlines most known ATX motherboard form factors in a simple guide.

 

  • Standard ATX (most of the time referred to as simply “ATX”)

    Standard ATX specifies length to be 12 inches with width varying from 6.7 to 9.6 inches.

    Maximum number of expansion slots is seven (7)

    Up to ten (10) mounting holes are available, although four of them are optional (circled in red)


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    ====== Form factors smaller than standard ATX motherboards =====

    Retail motherboards smaller than standard ATX motherboards will always be compatible with cases designed for standard ATX form factor.

    In order of decreasing sizes, they are:

  • Micro-ATX

    Micro-ATX specifies length to be 9.6 inches with width varying from 6.7 to 9.6 inches, it has three less expansion slots than standard ATX. Maximum number of expansion slots is four (4)

    Up to eight (8) mounting holes are available. The two holes circled in green are optional positions for motherboard manufacturers to utilize and holes circled in red are usually eliminated if the board size is small to not require them.

    Micro-ATX and ATX are the most common motherboard form factors

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  • DTX
     

     DTX

     Mini-DTX

    DTX specifies length to be 8 inches with width varying from 6.7 to 9.6 inches. Mini-DTX specifically refers to DTX motherboards with a width of 6.7 inches. Compared to Micro-ATX, DTX has two less expansion slots.

    Maximum number of expansion slots is two (2)

    Up to six (6) mounting holes are available. The holes circled in red are usually eliminated if the board size is small enough to not require them. Mini-DTX is the more common of the two DTX form factors

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  • Mini-ITX

    Mini-ITX specifies length to be 6.7 inches with width of 6.7 inches. It is the smallest form factor possible utilizing ATX mounting holes.

    Maximum number of expansion slot is one (1)

    All Mini-ITX motherboards use four (4) mounting holes, there are no known exceptions.


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  • Thin Mini-ITX

    Thin Mini-ITX has exact same mounting holes as standard Mini-ITX but with different rear I/O specification that is designed for thinner chassis. It is however, still compatible with cases designed for standard Mini-ITX. This form factor is the smallest of all ATX motherboards.


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    ========Form factors larger than standard ATX motherboards ======

    Motherboards larger than standard ATX will not be compatible with cases designed for standard ATX form factor.

    Cases designed for larger than standard ATX form factor will be compatible with standard ATX motherboards or smaller.

    In order of increasing sizes, they are:

  • SSI-CEB

    Standard SSI-CEB specifies length to be 12 inches with width varying from 9.6 to 10.5 inches. It is slightly wider than standard ATX.

    Maximum number of expansion slots is seven (7)

    Up to eight (8) mounting holes are available

    This form factor is common to lower end dual CPU motherboards

    Many ASUS ROG series motherboards have dimensions of 12 inches by 10.6 inches, which is slightly larger than CEB specification. Cases designed for CEB motherboards are generally compatible with ASUS ROG series motherboards such as RAVEN RV02 and Fortress FT02.

      ASUS ROG motherboard with dimensions of 12 inches by 10.6 inches

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  • SSI-EEB (most of the time referred to as Extended ATX or E-ATX)

    Standard SSI-EEB specifies length to be 12 inches with width varying from 10.5 to 13 inches. It is significantly wider than standard ATX.

    Maximum number of expansion slots is seven (7)

    Up to eleven (11) mounting holes are available

    This form factor is common to high end dual CPU motherboards

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  • SSI-MEB

    Standard SSI-MEB specifies length to be 16 inches with width of 13 inches. Compared to SSI-EEB, It is longer above the top to accommodate room for two additional CPU sockets.

    Maximum number of expansion slots is seven (7)

    Up to fourteen (14) mounting holes are available

    This form factor is common to quad CPU motherboards


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    ======Non-standard form factor motherboards =====

    Non-standard form factors are created by motherboard manufacturers for special applications

  • XL-ATX

    XL-ATX has length of 13.5 inches and width of 10.3

    Maximum number of expansion slots is nine (9)

    Up to twelve (12) mounting holes are available

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  • HPTX

    HPTX has length of 13.6 inches and width of 15

    Maximum number of expansion slots is nine (9)

    Up to seventeen (17) mounting holes are available

 
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