Found this, don't know if it'll help, it was on this website
http://www.dmccreative.co.uk/Education/How-To/Toolkits/Needlepoint-Toolkit.aspx?technique=crochet
SELECTING THE RIGHT NEEDLE
Tapestry needles are used in tapestry/needlepoint, because they have blunt tips and elongated eyes. The blunt tips pass smoothly between the fibres in the canvas and the elongated eyes accommodate the thicker threads used in tapestry/needlepoint. The size of the needle you will use depends on the size of the mesh of the canvas. For example, a narrow needle should be used on fine-mesh canvas, while a thicker needle is used on canvases with larger hole sizes. Select a needle that accommodates your thread and will enter the canvas with little or no drag on the thread. Tapestry Needles are sized by number and the bigger the number, the smaller or finer the needle. Refer to the DMC Needle Guide to see which needles are best for the thread being used.
8-10 count Canvas - use a size 16 tapestry needle
10-12 count Canvas - use a size 18 tapestry needle
12-14 count Canvas - use a size 20 tapestry needle
16-18 count canvas - use a size 22 tapestry needle