The size of one interior angle of a regular octagon is 135 degrees.
To find the size of one interior angle of a regular octagon, we can use the formula:
Interior angle = (180 * (n-2)) / n
where n is the number of sides of the polygon. In this case, n = 8 for an octagon.
Using the formula:
Interior angle = (180 * (8-2)) / 8
Interior angle = (180 * 6) / 8
Interior angle = 1080 / 8
Interior angle = 135 degrees
Therefore, the size of one interior angle of a regular octagon is 135 degrees.