Length: The length of the card, from it's video outputs to the back of the card.
Height: From the golden pins on the bottom to the top of the card (where the little ribbon cable comes out)
Thickness: the distance from the Left side of the card to the right side of the card when it's installed. e.g. from the edge of the left side, to the tip of the heatsink on the right side.
2 mins on Paint for your problem: