Root touch up kits(hair dye)

I bought one of these touch up kits last time I needed to redo my roots myself, and it was actually £1 more expensive than my usual haircolourant. It contained a little tray for mixing and a small angled application brush, along with a miniscule bottle of developer and a minisculr tube of colourant. Looking at it I felt I could surely do better by using just a proportion of my usual colourant so I kept the tray and brush. I needed to redo my roots tonight but was unsure how much of each to use, hence my search when I found previous post. I checked the amounts on the tubes and there was 50ml of colour and 40 ml developer, so I have mixed together a large plastic teaspoon of colour with a bit less developer. It produced the same amount of dye as the original touch up kit contained and I rekon there is enough left for about another 4 touch ups.