Yes — a footprint has to be slightly smaller than the tent floor, and this is the dimension people most often get backwards. A sheet that sticks out past the flysheet collects rain running off the fly and channels it under the tent, which is the opposite of the job it was bought for.
Why the rule runs that way
Water leaving a flysheet drips at the fly’s outer edge. If the groundsheet ends inside that line, the drip lands on the ground and drains away. If the groundsheet ends outside it, the drip lands on a waterproof sheet that is already under your tent floor, and the sheet becomes a shallow tray with your sleeping mat on top of it.
That is why the correct dimension is not “the same size as the floor” and certainly not “a bit bigger for coverage”.
Model-specific footprints
A footprint cut for a particular tent is made to the maker’s own plan and is already the right size. It usually carries ring-and-pin or webbing loops that share the tent’s peg points, so the fly and the footprint go down together — which is also what stops it shifting under the tent in wind.
Where you have that option, the sizing question disappears and the remaining decisions are fabric and weight.
Cutting your own
If you buy a universal sheet or cut from polycryo or builders’ sheeting, take the floor dimensions from the tent specification rather than measuring the pitched tent, since a pitched floor stretches. Then take 3 to 5 cm off each edge.
Round the corners slightly if the tent floor is not a rectangle. Most tent floors taper towards the foot, and a rectangular sheet under a tapered floor puts fabric outside the fly at exactly the widest point.
What else to read on the specification
Fabric is described by denier and by a stated hydrostatic head in millimetres, which is the maker’s waterproofness figure. Higher numbers usually mean thicker, heavier fabric, and this family runs from ultralight film through to heavy coated polyester.
Weigh that against packed weight and pack size, because a footprint is carried every day and used every night. It is one of the few pieces of kit whose entire job is to protect something else, so the weight has to be justified by the floor it is saving.
Does the footprint change the floor’s rating?
It adds a layer with its own stated hydrostatic head under a floor with its own. Makers publish both figures separately, and neither one is a rating for the pair — the numbers are not designed to be combined the way a mat’s R-value is.
What a footprint reliably does is take the abrasion. A tent floor is the expensive part; a footprint is the cheap part, and replacing the cheap part is the point.
The check before you order
Tent floor length and width from the specification, the footprint’s cut dimensions, whether it carries attachment points matching your tent’s peg points, its denier, its stated hydrostatic head, and its packed weight and size. If the cut dimensions are not published, that is a listing you cannot size from, and an oversized footprint funnels water to exactly where you are sleeping.
What people ask before buying
How much smaller should it be?
If you are cutting your own from sheeting, take the floor dimensions from the tent specification and cut 3 to 5 cm inside the tent floor on every edge. A model-specific footprint is already cut to the maker's own plan and needs no adjustment.
Can I fold an oversized footprint under instead?
You can, and it works as long as the fold stays tucked. The difficulty is that a folded edge creeps out overnight and forms a channel exactly where you do not want one. Cutting it down is the more reliable fix.
Last reviewed 6 September 2026