Tags :: §Shibari
The best width and diameter of Shibari rope is one of the most common beginner questions.
Broadly, people tie with ø3-8mm, and "long-rope" lengths from 5-10m, with the most common choice being ø6mm, 8m.
Common advice for length is to choose based on who you are tying - "I can complete a two-rope §box tie with x m of rope". However, especially if you are tying a lot of people, this isn't a very helpful yardstick. I agree with §Douglas Kent that the most important factor is your own arm length - you want to have a reasonable amount of rope while minimising the maximum length of a §pull-through. For many people this is 8m or slightly shorter.
People rarely keep only one length of rope; short rope is useful for finishing up ties or doing simple limb bindings. A common strategy is to half your long rope to get your short rope. Some people like to have many lengths (e.g. 8, 6, 4, 2), perhaps designated with coloured §rope whipping; however, I find that I cannot reliably tell between them and rarely take the time to check the whipping in the middle of a scene.
For diameter: the thinner your rope, the more precise and flexible it is likely to be, and the more pressure it will exert on the model. This means thin rope is less comfortable, giving it a more sadistic feel, which can be a turn-off or a selling-point depending on your perspective. Larger models often find thicker diameters more comfortable.
Personally, as I have a fairly small build, I like to tie with 7m or 7.5m. Anything longer than 8m feels "too long" to me. For my short ropes, I use 4m, as I find anything shorter can't be used usefully on its own. I like ø4-5mm, but often tie with ø6mm; anything thicker feels "too bulky" to me.