Quick answer: Yes. A ground tarp or footprint should be slightly smaller than the tent floor so it stays fully tucked under the edges. Marmot, a tent manufacturer, explains that a sheet which extends past the floor can collect rain and channel it beneath the tent, which defeats the purpose.
This is the most common footprint mistake. A big blue tarp feels like more protection, and it turns into a rain gutter aimed at your floor.
This guide explains the sizing rule, how to trim or fold a tarp, and what the layer is for.
Related: tent camping gear checklist, what to put under a tent and camping in the rain.
Why Smaller Wins
Rain running down the fly lands beside the tent. If the ground layer sticks out, water lands on it and runs under the floor, where it sits against the fabric. Tucked under, the layer stays dry on top and the water soaks into the ground around it.
How to Size a Tarp
- Pitch the tent and mark the floor outline on the tarp.
- Cut or fold the tarp about 2 inches inside that outline.
- Fold excess under itself, never out.
- Cover only the floor, not the vestibule.
What the Layer Does
| Does | Does not |
|---|---|
| Protects the floor from abrasion by rocks and sticks | Make the tent waterproof |
| Adds a barrier against damp soil | Replace good site selection |
| Extends floor life on gritty ground | Stop water pooling under a tent in a low spot |
Honest Limits
This follows one manufacturer guide. The 2-inch figure is practical advice, not a tested specification. Site drainage matters more than any ground layer.
Frequently Asked Questions
Should a tarp under a tent be bigger or smaller?
Slightly smaller, fully tucked under the floor.
Why not bigger?
It collects rain and channels it under the tent, per Marmot.
Can I just fold the extra under?
Yes. Fold it under, never out.
Does the tarp go over or under the tent?
This guide covers under. A tarp pitched above is a rain shelter and is sized differently.
How much smaller?
About 2 inches inside the floor edge is a practical margin.
Should it cover the vestibule?
No, only the floor.
Does a footprint make the tent waterproof?
No. It protects the floor from abrasion and damp.
Can I use a cheap plastic sheet?
Yes if sized and tucked properly.
What if water pools under anyway?
The site does not drain. Move the tent.
Do I always need one?
No. It helps most on gritty ground and with light floors.
Bottom Line
Keep the ground tarp slightly smaller than the floor and fully tucked.
Site drainage does more than any ground sheet.
Source: Marmot, What Is a Tent Footprint (manufacturer guide).