What Is a Three Quarter Bed? | Between Twin and Full

A three quarter bed is a mattress size measuring 48 inches wide by 75 inches long, fitting between a Twin and a Full in width and primarily used for antique frames, RVs, and custom setups.

If you inherited a vintage bed frame or need a mattress for your RV, you’ve likely run into the vague term “three quarter bed.” It’s not the standard name Americans use for modern sleep setups, but it still addresses a real problem: fitting a bed where a Twin is too narrow and a Full won’t fit the frame. Here is exactly what this size is, where it lives, and how to get the right mattress for yours.

Three Quarter Bed Dimensions and How They Compare

A standard three quarter mattress measures 48 inches wide by 75 inches long. That makes it the practical middle ground between a Twin (38 inches wide) and a Full or Double (53 to 54 inches wide). In the UK and Northern Europe, the same concept is usually 120 cm wide by 190 to 200 cm long, which is roughly 47 inches wide. In the US, the 48-by-75-inch spec is the modern custom standard, but antique manufacturers were not consistent — some frames require 48-by-74-inch or 48-by-72-inch mattresses.

Because it is no longer a mass-produced US size, you won’t find three quarter beds on the floor at major chain stores. They remain a specialty item for three main scenarios: antique Victorian or Edwardian bed frames, RV bunk configurations (often sold as “RV Three Quarter”), and custom-made sleep surfaces ordered through specialty makers. A single adult gets genuine extra room over a Twin without jumping to the full width of a Double. Two people can squeeze onto one in a pinch, but a Full is the better choice for regular shared use.

Where to Buy a Three Quarter Mattress in the US

Your best options are RV specialty retailers and custom mattress makers. Sleepy’s offers an 8-inch medium memory foam RV Three Quarter mattress currently priced at $499.99. Mattress Firm carries the same RV Three Quarter size. For antique frames, companies like CustomMattress.com, MyCustomBedding, and Mattress Insider handcraft 48-by-75-inch mattresses to fit older specifications. Amazon also carries a 47-by-72-inch sleeper sofa option, though that size falls outside the true three quarter standard.

Before you order anything, measure your existing frame — the biggest mistake is assuming all three quarter beds share exactly the same dimensions. Check our tested roundup of the best 3 quarter mattresses for current model recommendations and real-user feedback on fit and comfort.

Measuring an Antique Bed Frame for a Replacement

Because antique US manufacturers did not standardize this size, measuring your frame accurately is essential. Follow these four steps with a tape measure:

1. Measure length. Run the tape from the inside edge of the headboard to the inside edge of the footboard (or the end of the frame if there is no footboard).
2. Measure width. Record the inside width of the bed frame from one side rail to the other.
3. Measure depth. Measure from the base of the frame (the platform that supports the mattress) to the top of the side rails.
4. Sketch and contact experts. Draw a quick diagram with all three measurements and share it with a custom mattress maker to confirm the fit.

Common Mistakes and Compatibility Notes

The most frequent error is buying a standard Twin or Full sheet set for a three quarter bed — neither fits the 48-inch width correctly, and the result is a loose or bunching fitted sheet. You need dedicated 3/4 bedding, which is far easier to find in the UK than the US. Also remember that a UK three quarter (120 cm) is slightly narrower than the US standard (122 cm), so be cautious if ordering from overseas. Before moving a frame into a room, confirm you have at least 24 inches (60 cm) of clearance on one side for access.