On the driver side, I used an 8" and 12" strip. On the passenger side I used two 12" strips. If you can soldier, buy the full strip as I did. If you can't, you can buy them all individually but at a much higher cost. Most other sellers seem to sell them complete or in smaller pieces.
Here is where I bought them. Arrived in about 3 days after I purchased. Nice stuff:
LED STRIP FLEXIBLE SMD 3528 150 16FT WATERPROOF "WHITE" | eBay