Arabica is said to have less caffeine than Robusta. Couldn't find info about this specific question in Google hence asking here.
The grind I have is for filter coffee.
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The caffeine content of Arabica beans is around 1,2% of its mass. A standard measure of a teaspoon is approximately 5ml. That means you get around 5g of ground coffee in one teaspoon, which totals around 0,06g or 60mg of caffeine.
However please consider that teaspoons and spoons are in general a terrible unit of measurement for various reasons. Normal teaspoons are not standardized. American measuring spoons are close to 5ml but not 5ml. And in general they measure volume and not mass, which makes it dependent on the density of whatever you are measuring. For ground coffee this can vary widely and depends on the bean origin, the roast level, grind size and probably other factors I'm forgetting right now.
4 flat tsp of mixed blend of coffee from multiple sources weighted 3g. The powder was not packed/compressed at all.
1 packed tsp of the same coffe weighted also 3g.
My digital kitchen scale is able to measure only by 1g steps. I did multiple measurements +/- 1 tsp, at the end I concluded 1tsp of this particular blend is 1.67g. Therefore 1.2% of it is 20mg coffein.