How many square feet per chicken should coop be?

Hi all. I'm new to raising chickens and am wondering if the coop my husband built is too small. We just got three chicks and are planning on introducing them to the coop at about 6 weeks of age...in about a month. The coop is only 2'x3' though, plus a 2 square foot nesting box divided into two equal spaces. I'm worried it's not big enough for 3 large chickens. Hubby is awfully stubborn and I'll need a "second opinion" to get him to budge Any expert opinions would be welcome. Thanks in advance.