Where is a website I can find the square footage of a door, stairs, etc...?

Question

I am making blueprints of a house and I need to know these.

Answer 1

You don't need a website.  You multiple the length by width and that's the square footage.  If you are making blueprints, for instance with the stairs.  The square footage on your main view will not show the up and down of the stairs, only the length/width from where it starts to where it ends on the other side.  Try to see it as if the stair themselves weren't there only the hole.  Measure the hole and that's the measurement that you need for the main view.  

Then the second view, will show the measurements of the stairs themselves.  There are typical sizes for the risers (that's how tall each stair will be).  Your building supply can give you the size of riser that they sell.

I'd suggest picking up a Sunset Book on Construction, so you can sneak a quick glance without the computer.  Sunset Books are sold at Loews and Home Depot.  

Answer 2

Length times the width gives you the square footage. example average door is 2'6" X 6'8"= 17.68 square feet