The dimensions of this thing are clearly stated in the description, but I was still surprised at how large this dressing stone is. I love it! The large size provides plenty of real estate to move your stones around, while the entire face of the stone stays in contact with the dressing surface. It's also a good weight, so it will stay well planted on its rubber feet while you use it.
I used this to flatten a long neglected stone I've had for a long time and it's done a great job. I also bought some new Naniwa Super Stones with this, so will use it on those when needed. I'm super happy with this purchase.