A 14kB page can load much faster than a 15kB page. This is because of the TCP slow start algorithm: to determine the bandwidth between itself and the client the web server starts by sending 10 small TCP packets and waits for an ACK from the client.

The size of these packets is 1500 bytes. Each TCP packet uses 40 bytes in its header — 16 bytes for IP and an additional 24 bytes for TCP. That leaves 1460 bytes per TCP packet. 10 x 1460 = 14600 bytes or roughly 14kB!

Having a smaller website makes it load faster — that’s not surprising.

What is surprising is that a 14kB page can load much faster than a 15kB page — maybe 612ms faster — while the difference between a 15kB and a 16kB page is trivial.