I have my laptop with which I print out an quotation right there.
I measure the full room then adjust the price to take into account reduced cleaning area due to furniture or extreme heavy soiling etc. I tell my clients its 55 cents "per cleanable sf". Most rooms with beds etc I charge 30-25cents but based on the whole room sf. I like to keep the whole room measurement in my database.
A friend of mine uses a calculator and paper and writes out a quotation, he determines what percentage of floor space is cleanable and adjusts the square footage, then multiplies by the sf price.
Use a laser measure tool. I've been using a sonic tool and am going to upgrade to the laser. It impresses customers. Wheel tools are inaccurate, a tape measure is too old fashioned and too slow, and some times you may not have access to the whole room to use those tools. A laser is just two quick measurements, hit a button and it gives you the sf.
I'm looking at the Bosch tool, good for 130ft, less than $100
http://www.amazon.com/Bosch-DLR130K-Dig ... 396&sr=8-1