Each Chameleon Pen holds about 3.25 grams (or ml) of colored ink and the Mixing Chamber holds 3.25 grams (ml) of Colorless Toning Medium 

so together one Chameleon Pen houses about 6.5 grams (ml of ink!) 

Because you are mixing the Colorless Toning medium and the Colors every time you color with transition you essentially use 1/2 and 1/2 from each 

so the inks go a LONG way! 

The refills are 25ml will do 8-10 complete fills of pen and the 25ml of the Colorless Toning Medium will fill the Mixing chamber about 8-10 times 

but really you only want to add about 1 ML of ink at a time .. these are very juicy pens so you don't want to overfill. 

The ink refills will be available by end of the year but we will be posting videos on how to use the refill system by the end of this month