Are there any semi perm dyes that will cover very grey roots?

[BusStopBetty]

I can't get to the hairdressers for a few weeks and have used a nice and easy 24 wash dye, but the roots look barely covered. Admittedly I did use a lighter shade than usual as last time (using a perm dye) it went far too dark.

I did use the root touch up kit a few weeks ago, but is there enough in one of them to do your full head?

Any better suggestions?