How to size air conditioning unit without a load test

Once in a while you will may come across a situation where a customer would like to know which size unit they need, but no one knows the load of the particular building and a proper load test hasn’t been done yet.  As a temporary solution you could base a decent estimate off the square footage of the building. Our estimate calculation is 400 square feet per ton. For example, if a room is 50×50 or 2,500 square foot, we would estimate 6.25 tons for the proper temp change.  For tents, the estimate calculation is 100 square feet per ton. It also depends on the amount of air changes you need per hour,  and on the physical makeup of the individual building, which always makes a detailed walk down worthwhile.