.tiff is uncompressed data like bitmap - never use it on the Internet for web pages unless you enjoy wasting bandwidth. It's fine for a temporary phase, like scanning then editing something quite a bit, but not for a finished image for distribution. It's smaller if you're using black and white or grayscale, because there's very few colours to store, so it doesn't need to waste a full 24 or 32 bits per pixel. But then, if it's black and white or grey scale, you should be using gif or png with an appropriate colour palette instead, since they will do much better for that sort of image, since they will have lossless compression on top of all that.