King Mattress Toppers

A king mattress topper measures 76 by 80 inches, the same footprint as a king mattress. That makes it the widest standard size, 16 inches wider than a queen and exactly the same length, so the whole difference between the two beds is width.

No. A California king is 72 by 84 inches, so a standard king topper is 4 inches too wide and 4 inches too short at the same time. The two sizes are easy to mix up because both are called king, so order the cal king size if the bed is the longer, narrower one.

Probably not without checking. An RV king is commonly 72 by 80 inches, which is 4 inches narrower than a standard king and 4 inches shorter than a cal king, so neither standard size matches it exactly. RV bed sizes also vary between manufacturers, so measure the mattress before ordering. Viscosoft makes a queen short topper for RV beds in the smaller size.

It will cover the bed, but it defeats the purpose of a split. A split king is two twin XL halves at 38 by 80 inches each, and a single king topper spans both, which stops each side moving independently on an adjustable base. Two twin XL toppers sized to each half are the setup that keeps the split working.

Yes. Eastern king is the trade name for a standard king at 76 by 80 inches, and Western king is another name for a California king at 72 by 84. If a listing says Eastern king, a standard king topper is the right size.

No, it will overhang badly. A queen is 60 by 80 inches, so a king topper is 16 inches too wide even though the length matches exactly at 80 inches. The excess folds down the sides rather than lying flat, so the queen size is the one to order.

A California king, by four inches. A standard king is 80 inches long and a cal king is 84, so anyone over about six foot two gets more room at the foot of the bed on a cal king. The trade-off is width, since a cal king is 72 inches across against 76 on a standard king.

Match the thickness to how far off the mattress is rather than to the bed size. Two inches softens a surface that is nearly right, three inches noticeably changes the feel, and four inches suits a mattress that is genuinely too firm. Toppers thinner than 2 inches do very little, and anything past 4 inches tends to sit unstably, so the 3 inch king topper is where most people land.

Plan on two people. A king topper is the largest single piece of foam in the range, and once it has expanded it is awkward rather than heavy, so sliding it into position alone is difficult. Unroll it on top of the bare mattress before adding sheets, and give it a day to reach full loft before judging the feel.