Re: Capacity and Bus Dimensions
Counting windows will give you a rough estimate, but different manufacturers use different dimensions. Blue Bird uses 28" and 35", Thomas uses 27.75" and 37.75", AmTran uses 27.5", etc. A difference of an inch in window width can give you a difference of over a foot in bus length.
There's no standard dimension for a bus. Every manufacturer offers a variety of lengths with the same capacities to accommodate customer specs for legroom, extra equipment, sometimes even garage design. It makes it a pain in planning out a conversion, but the best thing to do is wait until you can get actual measurements from the bus you're looking at.
Rated capacities are based on 3 to a seat. Divide by 6 for the number of seat rows, which usually equals the number of windows (plus or minus one, depending on manufacturer). If it's one or two less than a multiple of 6, you have half-seats in the back to allow a wider aisle at the emergency door. The longest buses (after the seating standards in 1977) seat 90, not counting the driver. Before 77, some mid-engine models in California were built to hold 97. Most flat-nose (Type D) buses are built to hold 72 or 78. If you want to maximize your floor space, go for an 84 or 90 passenger.
Another example of a weird option: my bus was a 72 passenger built in a 78 pass body. Rear-engine buses usually have a rear pushout window and a left side emergency door. Sometimes they put a flip-seat by the side door, but mine had no seat there and extra legroom on the right. Long story short, the only way to know for sure is to measure the actual bus.