Ok, so I had to get it back out and measure it. I got it to sit still for one more picture, but then it scampered off. It didn't just creep like spiders are supposed to do. You could actually hear it's feet pattering on the floor. So here's the official measurement.

It's just over 10 cm! (That's about 4 inches to the non-metric folks) It could definitely take out a mouse. (The picture sticks off the screen a bit, but I did that because on my screen at least, that is actual size. Use a tape measure for your own comparison)