Before you cut any molding, measure the space it will fit into. There are two important tips to follow while measuring:

• Make sure you're at eye-level while measuring. Taking a reading from an angle, above, below, or to the sides, can result in an inaccurate measurement.
• It's always better to be a little long, than a little short. If you cut a piece too long, you can always go back and trim the piece to size later.