Several times I have been asked this question, so I hunted around and found a wonderful little calculator which can do this and much more.
It is called Project Calc. It is a regular calculator. Then it is a special calculator that will add, subtract, multiply and divide inches, feet and fractions of inches. I love that. They were really smart in designing it so you don't need the instruction booklet. You hit the buttons just like you talk. 4 (hit 4) inches (hit inches) times (hit multiply) 26 (hit numbers) equals (hit =) times (hit multiply) 5 (hit 5 ) feet ( hit feet) 3 (hit 3) inches ( hit inches) 5 (hit 5) (hit the fraction sign) 16ths (hit 16) equals (hit =) and it will tell you that you have a surface area of 6584.5 square inches.
After doing all of that you can convert surfaces or volumes into specific renovation quantities. If you wanted to know how much paint it will take to paint this area, hit convert and then the "Paint" button, and you will need .31 gallons. Of course it is all US imperial measurements, no metric.
If you multiply feet and or inches in thickness, width and length you will get cubic inches, which if you simply hit the convert button and then the board feet button you get board feet. Why do you want board feet? That is how wood is priced, by the cubic volume of wood before it was planed smooth. So if you have a 1 x 8 which is 14 feet long, you have 9.33 board feet.
The buttons are Board Feet, Studs, Roof Bundles, 4x8 sheets, paint, wallpaper, tile (all sizes), brick, blocks and gravel.
It is made by "Calculated Industries"