Measure both ridge ends before cutting cord

Draw each end as its own triangle

Measure the height of the ridge attachment relative to the intended anchor and the horizontal run between them. In an ideal flat setup with a ground-level anchor, the vertical difference is the ridge height. If the ground falls away or the anchor is higher, use that end’s actual height difference.

The straight segment is the square root of rise squared plus run squared. The guyline length guide derives the calculation. The A-frame geometry note uses a related triangle for the roof. That one has fabric length on the sloping side and answers a different question.

Work the lengths one end at a time

For a 1 m rise and a 1.2 m run, the diagonal is about 1.56 m. At the opposite end, a 1 m rise and 2 m run gives about 2.24 m. Even before tying, the second end needs about 68 cm more cord.

In Shelter Studio both end runs are assumed to be equal. The example tool produces the same diagonal for both, then includes corner lines and a general tying allowance. Use the symmetric estimate to get a first total, then measure what the real anchor positions would change. The run is the ground distance, so do not enter the diagonal in that box.

Leave space for the actual attachment

A loop, wrap or tensioner uses some cord beyond the direct line between attachment and anchor. Rehearse the tying allowance with the same gear. Note how much extra you need for adjustment without having to move the anchor. Add each allowance to its own end instead of assuming the two arrangements are identical.

Follow the manufacturer’s method and remember the cord material differences. A length estimate cannot select a reliable termination or approve a cord for safety-critical loading. A different diameter or hardware arrangement may change how much spare length you can actually use.

Check the route the cord takes

Stand at the places where people will approach the shelter. A workable distance on paper can put a line across a path or leave a tensioner in an awkward place to reach. If you move an anchor to correct that, measure the new run. Use durable locations and the relevant site rules when choosing where to pitch.

Mark the two lines or store them so the longer one is easy to identify. Test the whole setup before trimming a new line. For a trip with unfamiliar anchor spacing, keep an adjustable alternative rather than cutting only for the last place you camped.

Keep the measured rise and run next to the diagonal in your notes. That makes it easy to redo the estimate when a pole changes height or you pitch on a bench with a drop at one end. A note that only says “2.3 m” gives you no way to tell which change will make it too short.