Tarp Diamond Pitch Span Calculator

First, there’s the surprise geometry problem that snares most of us when we go camping. We purchase a rectangular tarp, pitch it as a diamond (which is just turning it 90°), and then the numbers fails to make any sort of sense. The dimensions you measured at the store no longer determine how big your shelter is. Instead, they’re replaced by diagonals. That switch from rectangle thinking to diagonal reality is what wrecks plans.

After all, you don’t need to guess if your ridge line fits between two tree. Once you input your specific dimensions into the calculator, it do the math for you.

How to Pitch Your Tarp Correctly

The other thing to know: What exactly do you have? Because a dozen by a dozen sounds like plenty of room, right? But pitched out from the corners in a triangle, that diagonal span will limit how big your shelter can gets. That diagonal is the hypotenuse of rectangle’s sides. It is always longer then the width or length alone. Know that number beforehand, so you shouldn’t of go home with one.

With a winged or otherwise custom cut tarp, you’ll want to measure the true distance from the high corners to the low stakes anyway. Either way, the tool will let you enter the direct diagonals or finished dimensions of rectangles, taking care of all the mental math for you so you can stop trying to convert square footage to straight lengths.

The one thing that makes all the difference is height. We have all heard that a taller ridge provide more head room, right? Yes, but it also provides for a broader footprint on the ground and a steeper pitch. When you increase the height of the ridge line you are battling the geometry of the fabric unless you adjust your side stakes. Your side stake corners stretches out to the ground. Now, the distance between your stakes and your ridge supports gets larger, and the panels themselves sits at an angle.

Flatter angles allow you to stand up easily. Steeper angles sheds water faster. It’s a trade-off, so you must choose based off the conditions. Do you want to be able to keep the heat off (high shade pitch)? Or do you want the water to stay off (low storm pitch)? You can’t have both at the same time.

The secret sauce that destroys even the best laid plans is stretch. Silnylon stretches. Silpoly doesn’t stretch as much. DCF basically doesn’t budge. So if you don’t account for it, by morning, your ridgerope with perfect tension will be stretched out like a wet noodle and sitting in a puddle. The fabric calculator accounts for stretch on various materials. And I’m telling you it’s not nothing. It’s the difference between having a soggy ground or a dry sleeping bag.

Leave yourself a bit of fabric at both ends of the ridge line. That’s what’s called an end drip clearance and keeps water from running down your pole and collecting under your head. This little tweak goes a long way to keep you comfy.

Geometry of the stakes is also important. If you set up too near the corner, it will have a shallow angle. Water runs off slowly and collects in the middle. Set up too far back for the pitch becomes overly complicated. Setting up with a modest setback provides good balance between tension and drainage.

The table on the page shows the usable span for various size tarps. Use this as a starting point to contrast with your site conditions. How do you know when to change it? That’s where the art comes in. When the wind blows out of the East, drop the East Ridge. Open the sides in a light rain. The numbers come from the calculator. How do you know which numbers to use? Experience.

Use the presets as a starting point if you don’t know. These have been made based off proven geometry that works in the field. After you learn how much side spread corresponds to how high off the ground the ridge sits, you’ll guess less. You’ll begin designing your shelter. It is all about respecting the diagonal.