Scratching-post-to-cat ratio = (number of scratching posts) / (number of cats)
Also, do your cats scratch the furniture?
Two cats, one post. One of the cats uses the post (and only the post), the other cat uses whatever he’s closest to when he feels the urge. So yeah, he uses the furniture. No noticeable damage though, after 10+ years. I guess that’s because he spreads the love, doesn’t focus on one piece of furniture. He really likes the carpet on the basement steps.
One cat, one post. For all the good it does; bastard scratches everything but the post.
We don’t have posts, as Their Sacred Majesties prefer the double-wide, catnip-infused luxury that is the Trader Joe’s scratchie box(that’s not my cat).
7 / 2
Not that I know of.
Yeah, I forgot to say, count any device designed to be scratched by cats as a scratching post for these purposes.
2 cats
1 very tall scratching post so they can stretch out to scratch - gets a lot of use
1 flat cardboard scratcher - gets moderate use
1 regular sized scratcher, hung on a doorknob in the hallway - a little use
My cats don’t scratch the furniture as a rule. Diego started scratching the top of a wooden chest, so I bought the flat cardboard scratcher which seems to be fulfilling his need to scratch on a flat surface (I still catch at him every now and then, but its much rarer).
When I got Diego and Serafina, I was very careful to train them to scratch their post. They will scratch their post on command for fish flake treats and they are overall very good kitties.
2 cats, 1 post.
Plus 3 chairs, one box spring, any hanging clothes, and occasionally my leg.
I’ve got five o’ dem bastids. We have rough cedar around our doorways. THey all love it. They’re slowly destroying the house, but they tend to stay away from the furniture (except for the cheap area rug, which one kitty has pretty much trashed).
Two cats:
Bern will not use the stratching post or the cardboard scratchy thing. She prefers the arms of the furniture, the footstool, and my right breast.
Cleo, she who is declawed, loves the stratching post and the cardboard scratchy thing. She also lays on the arm of the couch and claws the edge - we guess it SOUNDS like she’s doing something. She only drools on my breasts, thanks heavens.
3:1
Two cats. Two scratching posts on each floor of the house. Most of them are cardboard superscratchers.
And they don’t scratch the furniture at all. When they were young kittens, they did scratch up the bottoms of the couches and the bed. Fortunately, only in places that don’t show.
Both of my cats are determined not to scratch anything made for that purpose. The couch? Perfect for scratching! The scratching post? That is obviously not good enough for kitties.
So what’s your ratio?
1 cat and 1 post, it’s a combo plaything, scratching post and general perch to laze on and gaze imperiously at everyone. She doesn’t use the scratch post often, but it does get used.
Our living room furniture has a corduroy-like upholstery, she loves “scratching” it but doesn’t damage it, it’s more like claw massage. Fun to watch when she lays on the floor and drags herself the length of the couch by clawing along, yet she’s never left a mark on it.
There’s wicker furniture outside on the porch that she likes to scratch on, it’s like she knew it was okay because it was outside stuff so we’ve never bothered correcting her.
Infinite. We don’t have a post. Our cat only scratches at some plastic boxes, so we weren’t concerned about it. He leave furniture and fabric alone.
Actually zero. Infinite would be if you had a scratching post but no cat. 
So your ratio is 1:1, correct?
I have one of theseand three cats. They all love it and claw it and sleep on it and hide behind it and fight each other for it, though they wouldn’t touch it until I rubbed dried catnip into it.
They do not scratch furniture if they value their furry little lives, but they do claw area rugs. Of course, they go outdoors, too, where *everything’s *their scratching post.
Four cats and only one post, but it’s a really big one. They all use it to some degree.
None of them show much inclination to scratch elsewhere. There’s one spot on the horrible orange carpet on the basement stairs that is wearing just a bit thin, but I couldn’t care less about that carpet other wanting an excuse to get rid of it, so it all works out.
One cat, 2 Posts. And yes, she still scratches the furniture…
Two cats, one floor-to-celing cat condo with integrated scratching posts (never touched), six new and six to twelve used horizontal cardboard Bizzy Kitty scratchy pads at any one time, one shredded couch, and one very well ventilated leather desk chair. To be fair, the couch was abused by several previous cats.
One of the kitties loves nothing better than to show off by sharpening her oh-so-sharp claws right in front of you, so we put Bizzy Kitty refills in all the good posing spots. Then when they get ragged they go in the basement until recycling day.