Tent Footprint / Ground Tarp Calculator
Calculate the ground tarp (footprint) size needed for your tent, with a small margin trimmed back from the tent's actual edges so it doesn't collect rain water underneath.
How the tarp size is worked out
The margin is per edge, so it is applied twice on each dimension:
tarp length = tent length + 2 × margin
tarp width = tent width + 2 × marginWith the default two-person floor of 84 by 60 inches and a margin of -2, the tarp comes out at 80.0 by 56.0 inches - two inches lost off each of the four sides, or 6 ft 8 in by 4 ft 8 in of material. A margin of -2 does not shrink the sheet by 2 inches; it shrinks each dimension by 4.
Why the margin is negative
A footprint that reaches past the tent floor catches the rain running off the fly, and that water then sits in a puddle under your groundsheet. Keeping the tarp 1 to 3 inches inside the floor on every edge means the drips land on the ground instead. Positive margins are accepted, and are worth using only for a separate ground sheet you pitch under an open tarp shelter, where there is no fly shedding water onto it.
| Material | Weight for an 80 × 56 in sheet |
|---|---|
| Polycryo window film | 1.5-2 oz |
| Tyvek house wrap | 5-6 oz |
| Silnylon | 5-7 oz |
| Branded tent footprint | 8-11 oz |
Frequently asked questions
How much smaller should a tent footprint be?
One to three inches inside the floor on each edge. At two inches, an 84 by 60 inch tent takes an 80 by 56 inch sheet.
Do I need a footprint under my tent?
On gravel, roots or rough ground it saves the floor from abrasion and punctures, which is the expensive part of the tent to repair. On soft grass it is mostly extra weight.
What can I use instead of a tent footprint?
Polycryo window insulation film is the lightest at about 2 oz and costs a few dollars; Tyvek house wrap is tougher at 5 to 6 oz. Both cut to size with scissors and cost far less than a branded footprint.