Short answer
An end guy runs from the ridge end, at height h, to a stake at ground distance r, so its length is √(h² + r²). A 1.0 m ridge with a 1.5 m stake run needs a 1.80 m end guy. Add a ridgeline allowance for tree spacing, trunk wraps and knots, cut each line a little long, and trim after a test pitch.
A tarp needs three kinds of line. End guys run from each ridge end to a stake on the ground. A ridgeline joins two anchors, usually trees, and holds the ridge up. Corner and side tie-outs fix the edges. The end guy length follows directly from the ridge height and the stake distance. The ridgeline depends on how far apart the anchors are and how you tie off. Cut each line a little long, then trim it after a test pitch.
End guy length from ridge height and stake distance
An end guy is the hypotenuse of a right-angled triangle. One short side is the height of the ridge end above the ground, h. The other is the ground distance from the ridge end to the stake, r. The guy length is √(h² + r²), and its angle from the ground is atan(h ÷ r).
guy length = √(h² + r²)
example: h = 1.0 m, r = 1.5 m
= √(1.0² + 1.5²) = √(1.00 + 2.25) = √3.25 = 1.80 m
angle = atan(1.0 ÷ 1.5) = atan(0.667) = 33.7°
The stake distance r is measured on the ground, from the point directly beneath the ridge end to the stake. Measuring from the edge of the fabric instead adds the sag and the overhang, which the formula does not include. The table gives the end guy length for three ridge heights and three stake distances. Each cell is the same formula with its own h and r.
| Ridge height (h) | r = 1.0 m | r = 1.5 m | r = 2.0 m |
|---|---|---|---|
| 0.8 m | 1.28 m | 1.70 m | 2.15 m |
| 1.0 m | 1.41 m | 1.80 m | 2.24 m |
| 1.2 m | 1.56 m | 1.92 m | 2.33 m |
Steeper or shallower end guys
Ridge height and stake distance pull the guy in different directions. A higher ridge makes the guy longer and steeper, and a longer run makes it longer and shallower. Both changes add cord, but they affect the ground differently. At a 1.0 m ridge, the angle from the ground is 45.0° for a 1.0 m run, 33.7° for a 1.5 m run and 26.6° for a 2.0 m run (atan 0.5 = 26.6°).
A short run gives a steep, short guy and a small footprint on the ground. A long run gives a shallow, longer guy that needs more cord and more space around the stake. Neither the angle nor the length says how much load the stake or anchor will take. The model does not test that, and no safe working load is implied by any figure here.
Checking a guy you have already cut
The same formula runs in reverse. If the cord is already cut and the stake distance is known, the ridge height the guy can reach is h = √(g² − r²), where g is the guy length. Compare that height with the ridge height you want before you pitch. The formula only works when g is longer than r, because a guy shorter than its run cannot reach the ridge at all.
ridge height = √(g² − r²)
example: g = 1.80 m, r = 1.50 m
= √(1.80² − 1.50²) = √(3.24 − 2.25) = √0.99 = 0.995 m, about 1.0 m
The result is only as good as the measurements. A guy that is slack, a stretched line or a stake set a few centimetres off the planned point all give a different ridge height. Check the ridge height at the pitch itself, because the number from the cut length is a starting point.
Ridgeline between two trees
Between two trees, the ridgeline is the gap between the trunks, plus the wraps around each trunk, plus the knots. The Shelter studio does not model a ridgeline between trees, so the example below uses stated assumptions. The trunk centres are 5 m apart. Each trunk is 30 cm (0.30 m) across. The line wraps each trunk twice, and each end has a 0.5 m knot allowance.
span between trunk faces = 5.00 − 0.30 = 4.70 m circumference = π × 0.30 = 0.9425 m per wrap two wraps per trunk = 2 × 0.942 = 1.885 m two trunks = 2 × 1.885 = 3.770 m knot allowance = 2 × 0.50 = 1.00 m ridgeline cut = 4.70 + 3.77 + 1.00 = 9.47 m, about 9.5 m
Subtracting one trunk diameter from the spacing gives the gap between the two trunk faces, which is where the line runs. The wrap allowance is a planning figure. Bark, trunk shape and the way the line lies all change how much line a wrap really takes. Two wraps is a choice made for the example, not a rule for every tree.
Corner and side tie-outs
The Shelter studio's line estimate is illustrative. It counts two end guys, four 1.5 m corner lines and 2 m of tying allowance, with the end guy length taken from the same formula as above. Its inputs are the tarp width, length, ridge height and end guy run, which makes it a quick way to add up a whole pitch.
Worked example: a 3 × 3 m tarp at a 1.2 m ridge
Width 3 m, length 3 m, ridge 1.2 m, end guy stake distance 2.0 m. The corner lines are 1.5 m each and the tying allowance is 2 m.
end guy = √(1.2² + 2.0²) = √5.44 = 2.3324 m two end guys = 2 × 2.3324 = 4.6648 m corner lines = 4 × 1.50 = 6.00 m tying = 2.00 m total = 4.6648 + 6.00 + 2.00 = 12.66 m
That total is a planning figure, not a cut list for your pitch. The real tie-points depend on the trees, the stakes and where the edges sit on the ground. Cut the lines from the estimate, pitch the tarp, then measure what you actually used.
Knots and cord
Every end of the ridgeline and every guy needs a tie. The knot bench steps through a round turn and two half hitches on a practice post. It does not say what load a knot will hold, and it gives no working load or safety factor. For the knots themselves, see round turn and two half hitches and the figure-eight stopper knot. For the line, see guyline cord materials.
Cutting, testing and trimming
Cut each line a little longer than the estimate, so that a knot or a second wrap can be taken out later. The estimate cannot show how the tarp sits once the guys are tensioned, so pitch it once before you cut the last piece. A test pitch shows the ridge height you actually reach, the stake points and the line left over after the knots are tied.
After the test, shorten the lines to the real pitch and keep a spare length of cord for repairs. Re-check each line when the fabric sags, because sag lowers the ridge and changes the guy angle. The wind pitching guide covers re-tensioning in more detail.
Common questions
How long is a tarp end guy?
For a ridge height h and a stake distance r, the end guy is √(h² + r²). With h = 1.0 m and r = 1.5 m it is 1.80 m. Add the tie-off and knot allowance at each end before you cut, then check the real length after a test pitch.
Is a longer guy line better?
Not by itself. A longer run gives a shallower, longer guy and needs more ground space. The length says nothing about how well the stake or anchor holds, which the model does not test.
How much line for a ridgeline between two trees?
The planning example uses trunks 5 m apart with 30 cm trunks, two wraps each and 0.5 m per knot. That gives 9.47 m, cut to about 9.5 m. Real trees, wraps and knots will change the figure, so measure your own.
Should I cut guylines before or after a test pitch?
Cut them a little long, pitch the tarp, then trim. A test pitch shows the tie-points and ridge height you will use, which the planning numbers cannot show.
Sources
Published 2 November 2026. Reviewed 2 November 2026. Sources support the figures quoted; they do not endorse Trailwright. Report a correction through the owner’s contact page.