There are a number of web-based companies that supply bibs for displaying race numbers to organised events and sports clubs. If you're running a small sports event that requires participants to display race numbers and don't want to shell out money to buy bibs online, you can easily produce your own at home using basic computer equipment and stationary.
Open a new word processing document and type the number of the first race bib that you want to print.
Highlight the number and change the point size so that it covers as much of the page as possible. The size will depend on the font you're using, but somewhere between 500 and 700 point size is a good place to start for single-digit numbers. You may want to change the orientation of your document to landscape if you're printing larger numbers. You can change the font, point size and orientation of your document in the toolbar of most word processing programs
Load the A4 paper into your printer and click "Print."
Put the race number into the A4 clear plastic folder and seal. Make sure the number is clearly visible. The clear plastic folder can be attached to a competitor's clothing with safety pins.