How much cord do I need for my project?

First up, I have a video on this - watch it here 

This really depends on what you’re making... Ball park though? Plant hangers I would say you need about 20m for a simple hanger that’s approx. 1m long. Wall hangings - this varies a lot because of size and design elements. I would say start at approx. 30- 35m for a small and basic piece (for example - a wall piece thats approx 60cm long may use 16 x 1.5m lengths). The more knots and density to your pattern, the more cord you need!

ANSWERING THE AGE OLD QUESTION – HOW LONG IS A PIECE OF STRING?

There is no absolute answer for this - just an estimation method!

Now there are some very general sayings that you should use 3-5x the length of the desired length of your finished piece if the pattern is fairly open (meaning lots of gaps between knots) and approx 4-6x the length if the pattern is dense and closely knotted. 

Here is how I work mine out with a little more detail when I am trying to achieve a particular length.
I have found with cords that are approx 3-5mm thick, each knot usually takes up about 10cm of cord. To work length out, I estimate roughly how many knots I am going to need to tie on one piece of cord and multiply that by 10cm.
If you're attaching your cords with a larks head – remember each cord will need to be doubled over to give you two lengths when attached, so you'll need to double your calculation. Also, If you're looping it around an extra thick piece of wood make sure you account for that too.
In addition, I account for any length of cord that will remain straight within the piece, if there is any (i.e. any gaps between knots) and length of the fringe I want at the bottom.

See an example estimation at the end of this section.