A method of measuring dimension of a first pattern with a narrow first width, and a second pattern with a second width wider than the first width of the first pattern and formed in a symmetrical appearance with respect to the pattern center, the second pattern having edges opposed to each other defining the second width, includes a step of forming a pair of first dummy patterns each having a narrow width, the pair of first dummy patterns being spaced from the edges of the second pattern respectively by a distance approximate to the first width of the first pattern, a first measurement step of measuring, using a dimension measuring device, a spaced distance of one of the first dummy patterns from the edge of the second pattern and a width of the one of the first dummy patterns within the same field of view of the dimension measuring device, a second measurement step of measuring, using the dimension measuring device, a width of the first pattern under the same measurement condition as that of the first measurement step, and a calculation step of calculating a width of the second pattern from W.sub.B=2D.sub.A+W.sub.D+D.sub.C, where W.sub.B is the calculated width of the second pattern, D.sub.C is a design value of a distance between the centers of the pair of first dummy patterns, D.sub.A is a measured spaced distance of the one of the first dummy patterns, and W.sub.D is a measured width of the one of the first dummy patterns.