Search “Half Dome distance” and you’ll get three answers before you finish reading the first page. Wikipedia says 8.2 miles one way via the Mist Trail. A few paragraphs later on the same site, it says 8.5. The National Park Service quotes 16 miles — because they mean round trip, not one way, and nobody told you that up front. Same trail. Three numbers. None of them wrong.
That’s the actual problem with route distance: it’s not usually a bad measurement. It’s an unstated method. Fix the method and the number stops mattering as a mystery and starts mattering as a planning input.
Why the numbers never match
Three things move a distance figure without anyone lying:
- One way vs. round trip. The single most common mix-up. A “10-mile hike” that’s actually 5 miles each way reads completely differently on your legs.
- Which trailhead, which return path. Half Dome can go up and back on the Mist Trail, or up the Mist Trail and down the gentler John Muir Trail loop — different distance, different knee damage.
- How the line was traced. A straight ruler line between two GPS points undercounts every switchback. Trace the actual bends and the number climbs, sometimes by 15% or more on a zigzag approach.
None of that means the internet is unreliable. It means “how far is it” is really three questions wearing one trench coat.
Measure it yourself: the fast way
Skip eyeballing distance on a phone’s satellite view. Humans are bad at this — the eye smooths curves the trail doesn’t take, and switchbacks get flattened into something shorter and straighter than reality.
Instead, draw the route on our route planner. Click waypoints along the path and the tool measures the straight lines between them (the haversine formula, exact for whatever points you place). Turn on Snap to trails and each leg routes along real OpenStreetMap trail geometry instead of your rough clicks, so switchbacks count properly.
Elevation comes along for free. The planner samples about 100 points down your line, reads terrain height at each one, and totals the climbs — filtering out anything under 5 meters so GPS-style sensor noise doesn’t inflate the gain. That’s the same deadband trick handheld GPS units use. We’ve written about why gain figures disagree between sources; it’s the same story as distance, one level down.
Measure it the old way: paper and a scale bar
No signal? A topo map still works. Every USGS topographic map carries a scale bar — often 1:24,000, meaning one inch equals 2,000 feet on the ground. Lay a piece of string along the trail, following every bend, then straighten the string against the scale bar and read the distance off. It’s slower than a click-and-drag map tool, and it’s the method that keeps working when your battery doesn’t.
Running the number: Half Dome, worked out
Take the Mist Trail figures at face value: 8.2 miles one way, 4,800 feet of gain. Round trip, that’s 16.4 miles and the same 4,800 feet — Naismith’s math doesn’t model descent, so the climb only counts once. Feed that into the hiking time calculator on rocky terrain (granite steps and the cable section count as rocky, not easy trail):
| Fitness level | Estimated total time |
|---|---|
| Average hiker | ~14 hours |
| Fit hiker | ~12 h 20 min |
The NPS page says most hikers take 10 to 12 hours, some longer, and recommends a sunrise start with a non-negotiable turnaround time. Our “fit” column lands right in their range; “average” runs long. That gap is honest, not a bug — permit-holders self-select toward fitter hikers, and the granite steps near the cables are steeper than a generic “rocky” multiplier fully captures. Trust the range, not a single decimal.
The part worth remembering
Don’t trust a single guidebook figure for a route you haven’t checked yourself, especially on an out-and-back where one-way and round-trip numbers get quietly swapped. Measure it, know which of the three questions you just answered, and build in the margin the mountain will ask for anyway.
Draw the route before you drive to the trailhead.