I built a free calculator site for backyard chicken keepers — here's what I learned about coop maths

I recently shipped FlockCalc, a small site of free calculators for people who keep chickens, quail and ducks in their backyard. No accounts, no ads — just instant answers.

The interesting part wasn't the code, it was the maths arguments. Ask ten chicken keepers how much coop space a hen needs and you get ten answers. I ended up using the university extension figures: about 3.5 sq ft of coop and 10 sq ft of run for a standard hen, 2/6 for bantams, 4.5/12 for large breeds, 10 inches of roost per bird, and one nesting box per four hens.

That means the classic 4 × 8 ft coop honestly holds about 9 standard hens — not the 16–20 the box claims.

The most-used tool so far is the chicken coop size calculator. The one that surprised me is the cost per egg calculator: six hens on a $25 feed bag work out to roughly $0.22 an egg, which is cheaper than most people guess — until you add housing, then it isn't.

There are 14 calculators now (feed, hatch dates, brooders, quail cages, duck houses) plus a few written guides. Built with Next.js as fully static pages, so hosting is free and every page loads instantly.

If you keep birds, I'd love to know which number you'd argue with first.