We get this question frequently, but unfortunately the answer is difficult to estimate from a distance. This is because it depends on the patterns the tailor uses. For example, a long dress that is wide may need twice as much fabric as a long dress that runs tightly along the body. So always ask the tailor. It is also important to consider how the pattern runs, sometimes you want to use a design of a fabric in width, and sometimes in length. ( For example, with stripes, whether they will be horizontal or vertical on the garment.
Here are some rough estimates, purely to give an indication. Please do not use this as a basis for ordering the amount of fabric for your specific garment: a simple top 1-2 yards ( with sleeves maybe more ), a short skirt 2 yards, a midi skirt 3 yards, a maxi skirt 4 yards, a wide dress 5-6 yards.  These are purely indications, this is not advice!
So always ask your dressmaker!