I use Woolite instead - it's cheaper and comes with its own measuring ball! I've used it on lots of nuumed sheepskin saddlecloths, plus to hand wash our western saddle pads which are sheepkshin lined and it does a really good job.
Amymay - I bought the bottle when i bought the numnah yesterday, and have read it 5 x over and it doesn't say the only thing it does say is up to 15 washes, so my guess was like you said maybe just under a capful.