Rugs are sold in a fixed set of sizes, so the answer has to be one of them. Give us a room and we will find the largest standard rug that still leaves bare floor around it, or pick a bed and we will size the rug so your feet land on wool when you get up. Either way the answer is a rug that exists.
The answer has to be a rug that exists
Rugs are not made to order at the price most people want to pay. They come in a fixed set of sizes, and almost every room in the world falls between two of them. So the useful question is not what size rug would theoretically suit your room, it is which of the sizes actually sold is the right one. That is what this page does: it works out the ideal footprint and then snaps it to something you can put in a basket.
The standard set runs 3 by 5, 4 by 6, 5 by 8, 6 by 9, 8 by 10, 9 by 12, 10 by 14 and 12 by 15 feet, plus runners at 2 by 6 and 2 by 9. Those steps are big. Going from an 8 by 10 to a 9 by 12 adds nearly half again as much rug, which is why so many rooms end up with something too small: the next size up felt like a leap, and the smaller one was already expensive.
The formula
living room: largest standard rug leaving 6 to 18 in of floor all round
bedroom: smallest standard rug reaching 18 to 24 in past each side of the bed
never smaller than 12 in past the bed
In a living room the room is the constraint and the rule is about bare floor: under 6 inches and the rug looks like carpet that fell short, over 18 and it looks lost. In a bedroom the bed is the constraint and the rule is about where your feet land when you get up. Bed dimensions here are the same ones our bed size chart uses, so the two pages cannot disagree about how big a queen is.
Worked example
Take a 12 by 15 ft living room. Allowing the 12 inch design border on each side leaves 10 by 13 ft to work with, and the largest standard rug that fits inside that is a 9 by 12. That leaves 18 inches of floor at the sides and 18 at the ends, right at the top of the comfortable range. A 10 by 14 also physically fits, but it leaves 12 inches at the sides and only 6 at the ends, which is the absolute minimum and reads as much fuller. Either is defensible. What would be wrong is the 8 by 10 most people reach for, which leaves 2 feet of bare floor all round and makes a large room look like it is wearing a small hat.
Which legs go on the rug
Size and placement are the same decision, and the placement question comes down to furniture legs. There are three options and only two of them are good. All four legs of every seat on the rug is the most generous, most expensive version, and it needs a rug that runs past the furniture on every side. Front legs on, back legs off, is the workhorse: it ties the seating group together visually and needs perhaps one size less rug, which is why it is what most living rooms should do.
The third option, with the rug floating in the middle of the seating and nothing standing on it, is the one to avoid. It reads as a bath mat that got ambitious. The furniture looks like it is drifting apart, and the room looks smaller than it is, which is the exact opposite of what people are buying a rug to achieve.
In a bedroom, the top of the bed does not count
The instinct with a bedroom rug is to centre it under the bed, and that wastes a lot of rug. You never see the floor under the top third of a bed, because the bed is on it. Slide the rug down so it starts below the nightstands and runs out past the foot instead, and the same rug covers all the floor you actually walk on and looks considerably bigger doing it.
What you are aiming for is 18 to 24 inches of rug on each side, which is roughly the distance from getting out of bed to standing up. Below about 12 inches you step off onto bare floor, which defeats the purpose. A king is wide enough that hitting 18 inches on both sides needs a 10 by 14, which many bedrooms cannot take, so the honest answer at that size is usually a 9 by 12 and 16 inches, or a pair of runners down the sides instead.
When in doubt, go bigger
Of all the sizing advice on this site, this is the most one sided. Nobody has ever stood in a finished room and thought the rug was slightly too large. Too small is the mistake, it is extremely common, and it is expensive to fix because the answer is buying a second rug. If you are between two sizes and the larger one still leaves bare floor around it, that is your rug.
The one case where the arithmetic genuinely fails is a room that falls badly between standards, where the next size up will not leave any floor and the size down leaves more than 18 inches. That is the situation custom sizing exists for, and it is worth the money more often than people expect, because the alternative is spending nearly as much on a rug that will look wrong for as long as you own it.
Frequently asked questions
What size rug do I need for my living room?
Start from the room, not the furniture. Take the largest standard rug that still leaves 6 to 18 inches of bare floor around it, which in a 12 by 15 ft room is a 9 by 12. Then check the furniture: at minimum the front legs of the sofa and chairs should sit on the rug. A rug floating in the middle with no furniture on it is the mistake to avoid.
What size rug goes under a queen bed?
An 8 by 10 ft rug. A queen mattress is 60 by 80 inches, so an 8 by 10 leaves about 18 inches of rug on each side, which is the target: enough that your feet land on the rug rather than the floor. Slide it under the bottom two thirds of the bed rather than running it up to the headboard.
What size rug goes under a king bed?
A 9 by 12 ft rug in most rooms, or a 10 by 14 if the room can take it. A king is 76 inches wide, so a 9 by 12 gives about 16 inches on each side. That is slightly under the 18 inch target, and it is what most bedrooms can actually fit, which is why it is the standard answer.
Should all the furniture legs be on the rug?
Not necessarily, and this is where people overthink it. All four legs on is the most generous look and needs the biggest rug. Front legs on is the workhorse answer and right for most rooms, because it ties the seating group together without needing a rug the size of the floor. Nothing on the rug at all is the one that looks wrong.
How much floor should show around a rug?
Between 6 and 18 inches on each side. Under 6 and the rug reads as wall to wall carpet that did not quite make it. Over 18 and it reads as a rug that is too small for the room. If your room falls between two standard sizes and the gap comes out over 18 inches, that is the case where a custom size genuinely earns its cost.
Is it better to size a rug up or down?
Up, almost always. Too small is the single most common rug mistake, and it is the one that makes a room look smaller rather than larger. A rug slightly too big reads as a deliberate choice; a rug slightly too small reads as a budget decision. If you are between two sizes and the larger one still leaves bare floor, take the larger one.
Do I need a rug pad?
Yes, on any hard floor. It stops the rug sliding and creeping, it adds most of the underfoot softness people think they are buying when they pay for a thicker pile, and on wood it stops the rug backing abrading the finish. Buy the pad a couple of inches smaller than the rug on each side so no pad shows at the edges.
What about a runner instead of an area rug?
Runners are the right answer in two places: hallways, and beside a bed in a room too small for a rug underneath it. A pair of runners down each side of the bed gives you the same warm landing for your feet at a fraction of the rug, and in a small bedroom it often looks better than cramming in an area rug with no floor left around it.