Underpads are sold by overall size in inches, such as 23 x 36 or 30 x 36, and the right size depends on where the pad goes and how the person sleeps or sits. A pad that is too small leaves the sheet exposed, while one that is too big can bunch up. This guide matches common sizes to beds, chairs and sleeping positions so you can order with a tape measure instead of a guess.
Why underpad size matters more than you might expect
An underpad only protects the area it covers. Bodies shift during the night, and a pad that looked generous when you laid it down can end up under a knee instead of under the hips. The right size is often the difference between changing one pad and changing the whole bed.
Common underpad sizes and what each is meant for
These sizes appear in the titles of the pads we carry. They are overall dimensions in inches, with rounded centimetres alongside. Listings do not all give the two numbers in the same order, so check the product page before you rely on it.
| Overall size | About (cm) | Where it is commonly used |
|---|---|---|
| 17 x 24 in | 43 x 61 | A small pad for a chair seat, or an extra layer on top of a larger pad |
| 18 x 24 in | 46 x 61 | Chair seats and armchairs |
| 23 x 36 to 24 x 36 in | 58 to 61 x 91 | A mid-size pad placed under the hips and upper thighs in bed, or on a wider chair |
| 30 x 30 to 36 x 36 in | 76 x 76 to 91 x 91 | More coverage for people who move around in bed |
| 36 x 54 in | 91 x 137 | A large pad that covers more of the bed in one piece |
Both washable and disposable pads come in several of these sizes. Where more coverage is needed, there are extra-large listings such as Attends Supersorb XL Bariatric Underpad, 36 x 51 in.
Matching pad size to twin, double, queen and king beds
Mattress sizes are commonly listed at about 38 x 75 in for a twin, 54 x 75 in for a double, 60 x 80 in for a queen and 76 x 80 in for a king (about 97 x 191, 137 x 191, 152 x 203 and 193 x 203 cm). Mattresses vary by maker, so measure yours.
On a twin bed, a pad with a 36 in side, such as Reusable Underpad 36 x 54 in, Moderate Absorbency, reaches close to the full width when that side runs across the bed. On larger beds, a single pad covers only the zone where the person lies, so place it under the hips and upper thighs. Some listings name a bed size in the title instead of dimensions, such as Hygge Supplies Washable Incontinence Bed Pad, Bamboo Top, Queen Bed, so check the product page for the exact measurements. In a shared bed, the pad can go on one side only.
Sizes that work on chairs and vehicle seats
For a chair, measure the seat from side to side, between the arms if it has them, and from front to back. Compare both numbers with the compact sizes in the table: a pad wider than the gap between the arms rides up the sides and creases, and one that hangs over the front edge can slide.
In a car, a pad folded to suit the seat can work as long as it lies flat and never covers the seat belt buckle or the belt path. Keep the belt and its anchor points completely clear. For a child's car seat, check the seat maker's instructions before adding anything.
How sleeping position and movement change the size you need
Someone who stays on their back in the same spot needs less coverage than someone who rolls, curls up on their side or gets in and out of bed several times a night. For restless sleepers, go up one size from the minimum you measured.
If leaks are new or have changed suddenly, a different pad size will not explain why. Mention it to a doctor or nurse.
Overall size vs absorbent area on a washable pad
Some washable pads have fabric tuck-in flaps at the sides that go under the mattress to hold the pad in place. The flaps are not meant to soak anything up, so on those pads the absorbent centre can be narrower than the widest measurement. Listings differ on whether the size in the title includes the flaps.
If a product page lists the absorbent area separately, use that number to judge coverage and the overall size to judge fit on the bed. If it lists only one measurement and you are not sure what it describes, ask us before ordering.
A quick way to measure before you order
- Note where the hips and upper thighs rest when the person lies in their usual position.
- Measure the width and length of that zone, then add a few centimetres (an inch or two) on each side for movement.
- Compare that figure with the absorbent area where the page gives one, and with the overall size where it does not.
- If you fall between two sizes, think about which is the bigger risk for this person: bunching or gaps.
- For a washable pad, check that your washer and dryer can take the size you choose.
When you are ready to compare, many listings in the washable underpads and bed pads and disposable underpads collections give the size in the product title.
Shop this guide
- Incontinence Bed Pads Washable, Waterproof Chuck Pads (2 Pack, 34- x 36-) (ships via Amazon)
- Underpads: Ultrasorbs Underpads, 30" x 36"
- Utopia Bedding Washable Incontinence Bed Pads, 34 x 36 in, Blue, 4 Pack (ships via Amazon)
- Purenexus Health Disposable Underpads, 23 x 36 in, 50 Count (ships via Amazon)
- See all: Washable Underpads & Bed Pads
- See all: Disposable Underpads
Prices are on each product page. Free shipping on orders of $100 or more within Canada.
Common questions
Can I use two small pads instead of one large one?
Some households overlap two pads, but gaps and ridges can form where they meet. One pad that fits the zone is simpler to place and to change.
Is a bigger pad always safer?
Not always. A bigger pad has more fabric to bunch up and more to wash and dry, and a bigger disposable means more to throw away at each change.
Should the long side run across the bed or down it?
Either can work. Across the bed gives more side-to-side cover for someone who rolls, and down the bed gives more cover from waist to knee. If the pad has tuck-in flaps, they decide the direction.
Still unsure which size suits your bed or chair? Send us your measurements through our contact page and we will reply within one business day.