How long and wide is a Karate belt?
Karate belts are typically 1.5 inches (slightly less than 4 centimeters) wide and about 100 inches (2.56 meters) long. Your first belt is white and usually comes with the Karate Gi (Karate Uniform) that you purchased.

An interesting tidbit is that Karate belts usually have 8 lines of stitching running lengthwise along the belt. Cheap uniforms may come with belts that have only 6 lines of stitching. For some reason, black belts have usually 10 to 12 lines of stitching which makes the black Karate belt a little bit wider.

White and colored belts are usually made of cotton, whereas black belts often have a layer of satin over it. After all, the master has to look slightly more impressive than his students, and a little bit of satin may just achieve this :-)

If I need to buy a belt, how long should it be?
When you buy a Gi, the length of the supplied belt depends on the size of the Gi. Later on as you progress through the Karate belt ranking system, you will need to buy new ones in a variety of colors. Should your girth be out of the usual range for your height, you may need to purchase a longer or shorter belt to be able to tie it correctly. A good rule of thumb to calculate the length of belt needed is: required belt length equals approximately 3 times waist circumference.