Basic understanding

1 millimetre (mm) is the very tiniest unit of length on the common tape measure or ruler. This is the form of measurement we use most in framing being the most accurate.
1 centimetre (cm) is the unit of length going along the bottom of the example tape measure below. There are 10mm in 1cm.
1 inch (") is the unit of length going along the top of the example tape measure below. This is the most commonly used measurement in the United States. There are 25.4mm in 1 inch.

There are 148mm showing on this tape measure (or 14.8cm).

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Everyday examples

	Diameter of a CD or DVD: 120mm
	Length of a Bic Pen: 138mm
	Length of an envelope: 220mm

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Example of Frame vs Frame with Mat

When we have options of frames or frames with mats e.g. "8x12 inch Photo Frame" or "8x12 inch Photo Frame with Mat Border", the "8x12" refers to your actual picture size only. So for the frames with mat category, the mat border goes around the "8x12" picture and then the frame around that, therefore the frame is larger.

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Example of picture overlap

When framed, your picture is covered by approx 5mm around the edges. This is the "rebate".

When framed with a mat your picture is covered by approx 3mm - 5mm. It is important to have some overlap otherwise your picture would fall through the mat window (opening).

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Convert Inches to Millimetres

Conversion Tool Enter Inches    Value in Millimetres

For those posters/prints that have the inches written down the bottom (often from the USA) or where you know the inches but not mm, you can use this tool to convert Inches to Millimetres. NOTE: You must change a fraction of an inch to a decimal point e.g. 7¼ inches would be 7.25 inches.