What is the best pitch angle for rain?

A pitch angle of 35–50 degrees provides the best balance of rain shedding and usable space. Steeper angles (45–60°) shed rain better but reduce ground coverage. In heavy rain, pitch steeper and accept less space. In light rain, a flatter pitch gives more room.

How high should the ridgeline be?

For sitting comfort, 0.9–1.0m is minimum. For kneeling, 1.0–1.2m works well. For standing at the ridge, you need 1.5m+ which requires a larger tarp. Higher ridgelines reduce ground coverage unless you use a wider tarp.

How do I prevent water pooling on the tarp?

Ensure a steep enough pitch angle (35°+), keep the tarp taut with proper tensioning, and avoid flat spots. In heavy rain, create a slight catenary curve by not over-tensioning the ridgeline. Adding a drip line at the edge prevents water running onto your kit.

How long should guy lines be?

Guy line length depends on ridgeline height and stake angle. A 45° stake angle is ideal — it provides good holding power. Typically, ridge guy lines need to be 1.5–2.5m and mid-panel guy lines 1.0–1.5m. Always carry extra line.

CampCalcs

Rain Fly Angle Calculator

Calculate the optimal tarp pitch angle for rain shedding and ground coverage.

Tarp Length

Ridge direction length

Tarp Width

Side-to-side width

Ridgeline Height

Height of ridge from ground

Expected Rainfall

Fall factor calculation

How We Calculate This

Geometry

For an A-frame configuration, the tarp drapes over a ridgeline forming a triangle:

Pitch Angle = arcsin(Ridge Height / Half Tarp Width)

Ground Coverage Width = 2 x sqrt(Half Tarp Width\u00B2 \u2013 Ridge Height\u00B2)

Guy Lines

Guy Line Length = Ridge Height / sin(Stake Angle) + 0.3m (extra for knots and adjustment)

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Last updated: 2026-03-03

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.