For a Word or Powerpoint document
You probably need a GIF (.gif) or PNG (.png) file. These are ‘bitmap’ files (pictures made of dots), and will be easily imported by Office applications. Don’t use JPEG (.jpg) files – they are unsuitable for logos – they are intended for colour photographs. I prefer GIF or PNG files because they use up less disc space, but bigger BMP (.bmp) files are an alternative. You might also be able to use a EMF (enhanced metafile) format, which is a vector format and so has the advantages of the EPS file I describe below, but may be difficult for beginners to work with. You can make an EMF file with Adobe Illustrator. Here’s an interesting but quite advanced tutorial on how to set up stationery in Word
For a web page
For this you need a GIF or PNG file. Don’t try to scale it though! You should use it at its exact pixel size and ask for a new version if you want a different size.
Here the GIF file is all but useless. You need an EPS or PDF file. These are ‘Vector’ files. (see below) Because EPS files are big, I often convert them to PDF which results in a smaller file which is less likely to get corrupted when emailed. When I originally wrote this piece, it was still usual to send a Quark document together with the logo EPS to the printer, together with the fonts you used. Now professional designers usually supply a PDF file of the whole job. Although PDF is suitable for holding a single logo file, it can also be used for multipage documents with crops and bleeds and so is perfect for supplying print-ready artwork.
Bitmap files are made up of rows and columns of dots. When you enlarge them, you can see the dots. Examples are JPG, GIF, PNG, BMP.
GIF format logo
Blockyness when enlarging bitmap
BMP Bit Map Picture files are commonly used on Windows PCs. They are not suitable for transfer across the Internet, because they are poorly compressed.
EPS Encapsulated Postscript Files are vector files and used by printers, designers and other graphics professionals. Logos designed in Illustrator or Freehand (most are) will be originally in this format. From this file, you can make as many ‘bitmap’ versions at whatever size you choose. They are infinitely scalable.
GIF Graphic Interchange Format. This sort of bitmap file is very good for simple line art, logos and icons. It is rubbish for photos.
JPEG Joint Photographic Experts Group files are bitmaps which are great for photos but very poor for logos or text. See the side by side comparison below:
GIF format logo
JPEG format logo
PDF Portable Document Format are vector files and used by printers, designers and for general document distribution. They have all the advantages of EPS format and a smaller file size.
PNG Portable Network Graphics files are bitmap files. The format was invented to replace GIF which has problems with patent requirements. The format supports a wider range of options than GIF and is well supported by web browsers. It should not be used for professional print.
Vector files are made up of mathematically described geometric lines and shapes (rather than coloured dots) and so will never get ‘blocky’, whatever size you print them. Examples of vector formats are EPS, AI, PDF, EMF.