How to determine time to first byte?

I have been reading a lot about performance lately and there are tools which can assist you in increasing speed of a web page. But I could not find any tool that can tell me what is time to first byte for my web pages. Any hint?

Solution

WebPageTest.org is great but you can also use your browser dev tools to quickly check the TTFB. All your need is a network waterfall chart. Another method is to time your page render yourself.

Firefox

Firefox Net Panel

Chrome

Chrome Network Panel

Internet Explorer

Internet Explorer Network Panel