In order to measure a width of a wire a measuring pattern for the width of the wire is prepared. The measuring pattern includes: a first pattern with a first width; a second pattern connected to the first pattern and having a second width wider than the first width; and a third pattern connected to the second pattern and having a third width narrower than the first width. The first pattern, the second pattern and the third pattern are made of same material. The first pattern through a power source is connected to the third pattern. A first pair of probes are disposed on the first pattern and then are connected to a first voltmeter. A distance between the first pair of probes is a first distance wider than the first width. A second pair of probes are disposed on the second pattern and then are connected to a second voltmeter. A distance between the second pair of probes is a second distance wider than the first width. Thereafter the first width using gauged voltage at the first voltmeter and the second voltmeter is determined. The second width is more substantially ten times the first width and the third width is such narrow that current therethrough is uniform.