How long is the Pacific Crest Trail? The question is asked so frequently that we provide an answer on our most general PCT FAQ page. Here’s what we’ve been saying for the past few years:

The Pacific Crest Trail is 2,650 miles long. Is it? Probably not, but no one knows for sure. The tread moves every year, sometimes adding or subtracting miles at a time. Various places on the internet declare more specific lengths. Take them with a grain of salt. The PCT has never been mapped with tools that would provide a truly accurate distance for the trail. What data sets that do exist were generally gathered with consumer level tools and do not take in to account the various changes that happen every season. Years ago, PCTA decided to settle on a number. We can’t re-print t-shirts and remake trail signs every season as the tread moves. The Pacific Crest Trail is around 2,650 miles and that’s accurate to within 10 or so miles.

So, how many miles is the Pacific Crest Trail really?

Now, the PCT has been mapped with remarkably accurate tools.

Noodling around on the Halfmile dataset, I was stunned to see their most recent, most accurate, calculation for the length of the PCT registered in at 2,650.1 miles. I quickly fired off an email to the map makers telling them how blown over I was because the PCTA estimate of 2,650 miles was an educated guess at best and not based on any exact measurement. And of course, that all of the caveats above about signage and PCT products – and more – still apply to the latest number.

David Lippke, tech guru behind the Halfmile data, explained some of the details to me:

The total distance and the total elevation gain/loss are the very weakest of all our numbers. That’s because lots of tiny errors repeated hundreds of thousands of times can add up to some serious slop. Had I tweaked a certain data reduction epsilon just one thousandth of a meter it would have made the trail report in as shorter or longer. While those numbers are stronger than they’ve ever been, technically speaking, those particular metrics should be thought of as relatively weak. So let’s just keep saying 2,650 and call it a day. The accuracy focus when reported should be on this reality: the error between our electronic trail centerline and ground truth have now been made very small. And for almost every spot we now have an estimate for what the bounds on that error might be.

We know other things for sure: