A study of top sites by the HTTP Archive in San Francisco found the average Web page is now about 965 kilobytes in size, up 33 percent from 2010 when the average page was 726 kilobytes.
User demands for more images and interactivity as well as the tools used to track what happens when people visit a site are likely causes for the increase, experts said.
Large pages could take too long to load, leaving people frustrated and likely to go elsewhere, freelance Web developer Anna Debenham told the BBC.
However, there are ways to shrink the size of a Web page and ensure it loaded quickly, she said.
"There's always room for some optimization," she said, but added many Web developers are self-taught and relatively few are well-versed in techniques to reduce page sizes.
Slimmed-down Web pages will become more and more necessary as more people browse the Web on mobile devices, she said.
"We've had a bit of a lull where we all thought everyone was using fast broadband," she said. "But now we are almost back to where we were with dial-up because mobile speeds are so slow."