Getting a custom mattress size starts with measuring the inside of the bed frame, not the exterior, then ordering through a made-to-measure program.
Whether you’re fitting an antique bed, an RV, a boat, or an oddly shaped corner, a custom-size mattress is the way to make the space work. The process is straightforward: measure the usable interior space where the mattress will sit, note any unusual angles or corners, and submit those dimensions to a manufacturer that offers made-to-measure services. Several U.S. companies handle these orders, and the steps below walk through what to measure and how to order so the finished mattress fits the first time.
What Measurements Does A Custom Mattress Order Need?
Every custom mattress order starts with the same three numbers: width, length, and thickness. Measure the inside of the bed frame or sleep space—not the exterior rails—because that is the usable area the mattress must fill. For antique frames, measure from inside rail to inside rail.
Beyond the basic dimensions, note the shape details. If the mattress needs rounded corners, cut corners, angled sides, or post angles (common on four-poster beds), include those specifics. For anything beyond a simple rectangle, make a paper or cardboard template of the shape and provide it with the order. That template eliminates guesswork for both you and the manufacturer.
Thickness matters just as much as footprint. Make sure the depth you choose clears cabinet doors, walls, folding mechanisms, and the slats of antique or RV frames. Some vendors state their limits plainly: made-to-measure options usually fall between 4″ and 12″, with 8 to 10 inches common for RVs, daybeds, and antique beds.
The Custom Order Process, Step By Step
Each manufacturer runs its own custom-order flow, but the pattern is consistent. You start with a size, enter your dimensions, and get a quote.
- Foam by Mail has you pick a size, then enter your dimensions in inches. Round any fractional measurements up to the next whole inch so the mattress isn’t too small. Hit “Continue” to get your quote.
- Naturalmat UK asks you to select the size above your measured size, then choose “MTM – Yes” and enter your dimensions in cm. For a four-poster bed, measure the internal length and width along the slats, then add post dimensions and the post angle.
- Original Mattress Factory takes a more personal route: contact the nearest store or email your name, location, and contact info to start the custom-size conversation.
One crucial rule applies across sellers: do not round dimensions down unless the vendor explicitly says so. Foam by Mail states this outright—round up, and do not reduce measurements to compensate for the Dacron wrap. A slightly larger mattress fits; one that’s too small is useless.
Choosing A Size And Avoiding Common Mistakes
Most custom orders start from a standard base size that the manufacturer adjusts down to your needs. Some vendors require the next standard size up so they have material to cut away, so confirm that detail when you order. The standard U.S. mattress chart is the starting point for most custom work.
| Standard Size | Dimensions (inches) |
|---|---|
| Twin | 38 x 75 |
| Twin XL | 38 x 80 |
| Full / Double | 53 x 75 |
| Queen | 60 x 80 |
| King | 76 x 80 |
| California King | 72 x 84 |
The list hardly stops there. Custom manufacturers also handle 3/4 (48 x 75), Full XL (53 x 80), Olympic Queen (66 x 80), Split Queen (30 x 80 each), Split California King (36 x 84 each), Short Queen / RV Short Queen (60 x 75 or 60 x 74), Wyoming King (84 x 84), Texas King (80 x 98), Alberta or Vermont King (96 x 96), Alaskan King (108 x 108), and even a Family Bed (120 x 84). Waterbed sizes and boat shapes with unusual angles are also available in the U.S.
Pricing for custom work comes by quote, not by listed price. Some options start “From $249”, but be ready for a service fee: one vendor charges a $750 service fee and requires the base standard mattress to be larger than the custom size so it can be reduced down. Always confirm fees before you commit.
The mistakes that sink custom orders are easy to avoid. Do not assume a standard size fits an unusual frame. Do not round fractional inches down when the seller says round up. Do not skip the thickness check. Do not omit corner geometry—angled, rounded, or cut corners need a template. And never rely on exterior frame measurements when the vendor asks for the inside usable space. If you’re ready to compare specific models and brands that offer this service, our roundup of the best custom-size mattresses breaks down the top options side by side.
The payoff for careful measuring is a mattress that looks like it was built with the frame in mind—because it was. Take the measurements twice, note the corners, pick the thickness, and let the quote process confirm the numbers before you order.
FAQs
Can I order a custom mattress for a boat or RV?
Yes. U.S. manufacturers handle custom sizes for boats and RVs, including shapes with unusual angles. Most require the same measurements as any custom order—width, length, and thickness—plus a paper template if the shape is anything beyond a simple rectangle. RV short queens and split sizes are common requests.
Should I round my measurements up or down?
Round up. Foam by Mail explicitly instructs customers to round fractional dimensions up to the next whole inch so the finished mattress isn’t too small. Follow each seller’s instructions, but when in doubt, err on the larger side. A slightly oversized mattress fits better than one that leaves a gap.
How much does a custom-size mattress cost?
Custom mattresses are quoted individually, so prices vary widely. Some options start around $249, but service fees can add hundreds. Always request a quote before ordering and confirm all fees upfront.
References & Sources
- Foam by Mail. “Custom Foam Mattresses.” Details on ordering custom foam mattresses by size, with rounding instructions and quote workflow.
- Naturalmat. “Made to Measure Mattresses.” Official guide for MTM orders, four-poster measurements, and dimension formats.
- Original Mattress Factory. “Custom Size Mattresses.” Explains the custom-size process, service fees, and the requirement to start from a larger standard size.