Why should I get a footprint for my tent instead of a general use tarp from my local hardware store?
A footprint will extend the life of your tent by providing an extra layer of fabric from debris you might miss and an additional layer of protection from moisture in the soil/grass that will condensate on the bottom of your tent
That said you should go to the hardware store and make your own
matched footprint. Stand by for some simple directions and save yourself some money from buying the optional footprint and an exceptional amount of satisfaction by making your own. Do it now before you forget; go on - hop in the car and go to Lowe's or HD.
Purchase (1) a tarp that's a little bit bigger than the tent's floor dimensions. Don't be angry that it's too big and that there will be some extra that is "unusable." You'll save that extra unusable piece and use it as a ground cloth for field repairs on your vehicle to protect your clothes or catch nuts and bolts you'll lose control - it will be a much more practical size instead of a big old tarp that will get flooded with rainwater (vehicles typically break in foul weather according to Murphy's Law). If it has a reflective light-colored side - bonus - that reflected light will come in handy when working under your truck. You'll always keep this extra patch of tarp tucked in some out of the way space in the truck. Next, get a (2) grommet kit. Finally, get a (3) roll of 1-inch flat braided nylon - you know like backpack strap material. This ain't rocket surgery... 3 items.
Erect you tent. Flatten out your much larger new tarp and be sure to get as many wrinkles/folds out. Set the tent on the tarp. Most tarps have a bound edge and grommets at the corners. I don't like them so I cut them out. Weight the tarp so it doesn't move around. Take you scissors and cut around the base of the tent - straight enough is good enough.
Clear the area of discarded tarp material. Prepare the nylon straps. Cut at least 4 (for each corner if it's a rectangular or square tent; other geometric shapes might require 5 or 6 straps) nylon straps of 10 inches. Fold each strap in half and affix the strap to each corner of the tarp with a grommet bisecting the corner, extending the strap in about 2 inches. Don't forget to take a lighter and singe the edges to keep them from fraying - rookie mistake. Place another grommet about 1 inch from the folded edge. Do the other 3, 4, or 5 corners, and Bob's your uncle.
Now the tent pole will be inserted into the tarp grommet and tie into the tent floor base structure together, keeping both taught. You'll see this folds up nice and compact and will fit in the same kit bag you have your tent in. If you have a different tent, like an Oz tent with a potential for a screened in room, you can extend this ground cloth footprint to the screen room for a floor in that area as well with additional grommets to tie in to that system. For those of us who live in areas with rainy and muddy conditions with greater frequency than our West coast colleagues, this is the way we stay dry and free from mud.
I've been doing this for years with all my tents. Far better than any brand-name footprint you can purchase, and far more durable. Do it now before you forget and it's time to hit the road - you do not want me to nag you. I'm a retired Navy Nurse Corps Officer - I've learned from some of the best nags in the Navy.