The bed has its own reorder, and it does not run on the same calendar as briefs. Disposable underpads arrive as a counted case. You take one sheet, use it, and throw it away. Washable bed pads are cloth. They go to the washer and come back. If you reorder for yourself or for a parent, keep them as two lines.
Inches decide if two pads are the same errand. When the article was written, Amazon showed three cuts at three prices. Medline Ultrasorbs disposable underpads, 30 by 36 inches, 70 count, were $121.00. A washable waterproof pad, 36 by 76 inches, with tuck-in sides, listed for king and California king beds, was $39.99. A PRIVA washable pad, 17 by 22 inches, one pack, was $9.65. The PRIVA sheet is small. The 36 by 76 inch pad is a long layer for a king bed. A cart that ignores the inches can land the wrong shape.

Check the Amazon listing before buying; its price, count, and size may have changed since this article was written.
For a per-sheet figure on the disposable case, divide the price on that page by the count on that page. $121.00 divided by 70 is about $1.73. It moves when the case price moves. Price per piece, not price per pack covers the same division on other counted bags. The washable listings here are one pad each. They do not print a number of washes, so the price stays the price of the pad.
Disposable cases empty by the sheet
The Medline title calls the product a disposable adult underpad and also uses chucks and chux. The recorded description says the backsheet does not let liquid through, and that the pad is meant to keep a mattress or another surface dry. “Premium ultra thick” and “full body coverage” sit in the title. Amazon showed that recorded price of $121.00 when the article was written. The listing is Medline Ultrasorbs disposable underpads, 30 by 36 inches, 70 count.

A house that uses several sheets a day empties a 70-count case sooner than a house that uses a sheet only on some nights. The stack shows it. If the cut still fits, the next order is another disposable case in those inches. A shorter bag at a lower unit price is a size change, even if the title still says underpad. These sheets are not washed and put back. The supply note needs disposable, the inches, and the count. A photo of the empty bag usually has all three. Brand alone is a weak match when one name covers more than one size.
Washable pads wait on laundry day
The 36 by 76 inch washable pad is a single piece with tuck-in sides. The listing says those sides let it stand in for a mattress protector, and the page names king and California king beds. That wording belongs to this product. A mattress protector is still a separate item, and people often buy one in the same order as a bed pad. Mattress protectors and bed pads keeps the two names apart. The PRIVA pad is washable and waterproof on its listing, at 17 by 22 inches, and the recorded note treats it as a small pad, not a cover for the whole mattress.
Amazon showed that recorded price of $39.99 when the article was written for the 36 by 76 inch reusable bed pad with tuck-ins. Amazon showed that recorded price of $9.65 when the article was written for the PRIVA 17 by 22 inch washable pad. Several small pads do not add up to one long pad. If the bed is a king, the reorder has to say so in inches.
How many washable pads to keep depends on how often the washer runs. You need a dry one ready after a wet one comes off. If the label prints a wash or dryer setting, follow that label. A plastic back or a cloth-like back on a throwaway sheet is a separate choice, covered in plastic-backed and cloth-backed underpads. The wider bed-layer list is bed pads and mattress covers for nighttime leaks. An order can include a washable pad for everyday and a disposable case for when laundry is behind. Keep those as separate lines.