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.
Ground coffee density is 365 kg/m³, so it's 2,72 times less dense than water, therefore 5 ml of ground coffee means 1.83 g, which equals to 22 mg of caffeine if the concentration is 1,2%.