Okay, the images in today's review were a good joke, but you still deserve to see the full image, not cut into long shards:
And now, what you really want: math!
If Wilbur Day is 5'6" without his armor, then his inseam is probably about 27" - adding the height of his feet, call it 30" from hip to the ground. To calculate your stride length, pedometers and fitness trackers multiply a man's height in inches by 0.415 (or 0.413 for women), which gives Wilbur a rough estimate of a 27" stride. With two legs that meet at the hip and also both touch the ground, we've got ourselves a triangle!
Using the Law of Cosines [(b² + c² - a²) / 2bc] we can plug in the numbers and find the angles of this triangle - since the internal angles of a triangle will always add up to 180°, and we know the two at the ground would be the same, we just need to solve for the top angle, subtract that number from 180, then divide the result in two. Rounding off a little bit, we get 53.5° at the hip and 63.25° at the feet.
Now let's reverse that. Knowing all the angles, and accounting for the fact his stilts extends to 250', we can determine exactly how far a single step would take Stilt-Man at max height: 225 feet, or 75 yards per stride.
If you're very clever, you may notice that 250' feet is 3,000 inches, and thus exactly 100 times greater than his usual 30" legs, meaning you don't even have to do all the stuff with the angles, and instead save yourself some time and effort by just adding two zeroes to the end of any measurement to properly scale it up. For instance, if an average walking speed is three and a half miles per hour, then Stilt-Man is moving 350mph by taking a casual stroll through the city. He could walk from New York to Toronto in that time. Imagine if he tried running! Or even just walking at a brisk pace. Even at an amble, he's already faster than a baseline Quicksilver, so who's going to catch him?