On Monday, June 13, 2016 at 8:29:16 PM UTC-5, wrote:

is poplar a strong enough wood to support a large granite countertop?

8"across top 14 5/32 down the side 3" thick

An average countertop is usually about 25" deep. I wouldn't trust 10, of that size corbel, to support a countertop of 6' length or more.

What's the size and thickness of the countertop?

Sonny