1/2 the reported wind if its 30 degrees off = the crosswind (1/2,3)
2/3 the reported wind if its 40 degrees off = the crosswind (2/3,4)
3/4 the reported wind if its 50 degrees off = the crosswind (3/4,5)
...and any more than that its pretty much all crosswind (apparently).
I think this is too coarse, and here is why.
50 degrees off is .75 of the stated windspeed <<and any more than that its pretty much all crosswind (apparently)>> No it isn't? You are in error by up to 25% of the stated windspeed!
60 degrees is 87%
75 degrees is 97% (now we are getting to 'pretty much all crosswind').
You can be easily in error your way by up to about 20% of the wind, which for a 40kt crosswind limitation could see you having to go around because of an error you have made in your calculation of 8kts when you could legally have landed! My suggested method above is highly accurate- all it takes is learning a few numbers! It will give you bang on the actual crosswind, not a poor approximation.