Generally speaking the hackle should be one and one half times the distance of the gap of the hook. Accuracy and ease in obtaining this important measurement is gained by use of a hackle gauge. Several styles of hackle gauges are available and beginning fly tiers should use one to ensure their fly proportions remain consistent from one fly to the next. As you progress into fly tying and become proficient in the required skills, you may develop a need for more tools. The same theories of purchase should apply.
Tools are a life long investment .