This depends entirely on what purpose the concrete is intended to serve. For the weakest concrete useable for example as load bearing fill you could use less than 100kg of cement per cubic metre, for very strong structural concrete it would exced 300kg per cubic metre.
Do you mean a length of 1.9m. If so we need to know the volume. If you mean 1.9 cubic metres, thats about 4.1 tonnes which is a hell of a lot of knocking up! You'd be better off ordering it ona mini mixer or an on site mixer truck (like Mix a mate used to be).
yeah 1.9 cubic i have ordered it now and will knock it up by hand will take a few hours but should be ok i knock it up at work but never this much but im sure all will be ok