Custom Mattress for an Antique Bed: How to Measure and Get a Good Fit

Why don't modern mattresses fit antique beds?

An heirloom bed might be the one your grandparents slept in, or a find from an estate sale. The trouble starts when you shop for a mattress.

The Sleep Foundation explains that mattress width and length are standardized for each size today, while thickness varies by maker and model. Older beds were not always built to those numbers. Some are close to a modern full or twin. Others fall in between. One in-between size is the three-quarter, at 48 inches wide.

Some old beds take a standard mattress with no trouble. When yours doesn't, a mattress can be made to the frame. Here's how the standard sizes compare, so you can see where your measurements land.

Sizes from the Sleep Foundation. The six standard sizes are the ones listed on our mattress pages. A three-quarter size, or any size that isn't on the chart, is the kind of order a custom mattress is for.

How do you measure an antique bed for a mattress?

Take the old mattress out first, so you measure the frame itself. A steel tape measure works better than a cloth one.

1. Width. Measure between the inside faces of the side rails at the head, the middle and the foot. Old frames are not always square, so use the smallest of the three numbers.
2. Length. Measure from the inside of the headboard to the inside of the footboard, at the height where the mattress will sit. Posts and trim can stick in, so measure along both sides.
3. Rail depth. Measure from the top of the side rail down to whatever holds the mattress up. This tells you how much of the mattress will sit inside the frame and how much will show above it.
4. Footboard height. Measure how far the top of the footboard rises above the support. A low footboard can disappear behind a thick mattress.
5. Support. Note what the mattress will rest on: wood slats, a solid platform, metal springs, or nothing yet. Count the slats and measure the gaps between them.

Write your numbers down as width x length x rail depth, and take a photo of the frame with the tape in it. Give the mattress maker the exact inside measurements and ask how much they allow for an easy fit. Don't round them yourself.

Check the bedding, too

Sheets are easy to forget. The Sleep Foundation notes that thicker mattresses may need sheets with deep pockets. For a three-quarter or other odd size, plan on custom sheets as part of the job.

How thick should a mattress be for an antique bed?

There's no single right number. It depends on how deep the rails are, how tall the footboard is, and how high you want to sit. Mattresses vary a lot. The 18 mattress pages on our site list heights from 9 to 17 inches, depending on the model and feel.

A few rules of thumb help:

• Low footboard? A thinner mattress keeps the footboard in view. Our Resilience Luxe and Resilience Premier are both listed at 10 inches.
• High bed? Many antique beds already sit high. A thick mattress on a full box spring can make the bed hard to climb into.
• Built-in limits. Some beds are designed for a mattress of a certain thickness. Our Murphy wall beds, for example, list a recommended mattress thickness of 10 inches.
• Bunk beds. The U.S. Consumer Product Safety Commission requires bunk bed guardrails to reach at least 5 inches above the top of the mattress. A thicker mattress than the bed was designed for can cut into that margin.

What goes under the mattress

The foundation changes the height too. On our mattress pages, all 18 models offer a standard-height or low-profile 14-slat foundation, or a bunkie board with 8 or 14 slats. Five also offer an 81-coil box spring. A low-profile foundation or a bunkie board is the thinner choice when the rails are shallow.

Whatever you choose, tell your salesperson what the mattress will sit on: slats, a foundation, a box spring or an adjustable base. It changes what fits and what we recommend.

Can you get a custom size mattress from us?

Yes. Our site lists 18 mattresses on the mattresses page, and 17 of their pages say "Custom sizes available by special order." Each one is listed in the six standard sizes, from twin to California king, so a custom size covers the beds in between.

The pages also list each model's height, whether it is single or double sided, and a firmness number on the maker's own scale, where 1 is the most plush and 8 the most firm. Ten of the 18 pages list the mattress as double sided, so it can be flipped. A few examples:

• The Elite is double sided, listed at 13 inches in plush and 10½ inches in firm.
• The Resilience has a pocket coil innerspring core and is listed at 12 inches.
• The Resilience Luxe is natural Talalay latex from top to core, at 10 inches.
• The Integrity Essential uses high-density poly foam and comes in plush, firm and extra firm at 13 inches.

To start a custom order, bring your measurements and the photo of your frame to one of our showrooms, or call us. If you're not sure which feel you like, our mattress quiz is a quick way to narrow it down.

What kind of mattress helps with back pain?

A firm mattress is commonly believed to help a sore back. The research doesn't back that up.

In a well-known trial published in The Lancet, 313 adults with chronic low back pain were given either a firm or a medium-firm mattress. After 90 days, the medium-firm group had better results for pain in bed, pain on getting up, and disability. A 2021 review of 39 studies came to a similar conclusion: a medium-firm mattress supported comfort, sleep quality and spine alignment.

Two cautions. First, firmness scales are not the same from one maker to the next. The scale in that trial is not the 1 to 8 scale on our mattress pages, so the numbers don't translate. Lie on a mattress in the position you sleep in before you decide. Second, a mattress is not a treatment. If back pain keeps you up or lasts, talk to your doctor.

Fit plays a part too. A mattress that is too small for an old frame can slide, and one that is squeezed in can bulge. The right size sits flat and stays put.

Should you keep the antique bed or choose a new one?

If the frame is sound and you love it, a custom mattress is usually the simpler fix. If the rails are cracked, the support is gone, or you need a bigger bed, a new frame may make more sense. Our wood furniture care guide covers how to keep an older piece in good shape.

New beds take the guesswork out, because the sizes are listed. Of the 139 beds on our beds page, 135 come in full and queen, 133 in king, 99 in California king and 72 in twin. Many pages also list the height to the mattress. On 41 of our Millcraft bed pages, the top of the slats sits 11¼ inches off the floor, and the Hamilton Panel Bed is shown with a low-profile mattress. Most of our furniture is made to order, so you can choose the wood and finish. If you're shopping for a whole room, see our guide to choosing a king bedroom set and our solid wood bedroom furniture guide.

Mattresses with custom sizes by special order

See all our mattresses and beds, or read what to expect when you visit our showrooms in Intercourse and Lancaster, Pennsylvania, and Murrells Inlet, South Carolina.

Frequently asked questions

What size is an antique bed?

It varies. Some are close to a modern full, which is 54 by 75 inches. Others are three-quarter beds, about 48 inches wide. The only way to know is to measure the inside of the frame.

Will a full mattress fit an antique double bed?

Sometimes. The Sleep Foundation notes that a full is also called a double. But older double beds were not always built to today's 54 by 75 inches, so measure width and length before you buy.

Can I put a box spring in an antique bed?

It depends on how deep the rails are and how high you want the bed. If a full box spring makes the bed too tall, a low-profile foundation or a bunkie board is a thinner option.

What firmness is good for back pain?

Studies, including a trial of 313 adults with chronic low back pain, found medium-firm mattresses did better than firm ones. Try the feel in person, and see a doctor about pain that doesn't go away.

Do you make custom size mattresses?

17 of the 18 mattresses on our site list custom sizes by special order. Bring your measurements to our showroom at 13 Center Street in Intercourse, 2460 Lincoln Highway East in Lancaster, or 12052 Highway 17 Bypass North in Murrells Inlet. The Pennsylvania showrooms are open Monday to Friday 10 to 5 and Saturday 9 to 5.

Sources

• Sleep Foundation: Mattress Sizes
• Sleep Foundation: RV Mattress Sizes (three-quarter size)
• Sleep Foundation: Full Size Bed Dimensions
• Kovacs et al., The Lancet (2003): Effect of firmness of mattress on chronic non-specific low-back pain
• Caggiari et al., Journal of Orthopaedics and Traumatology (2021): What type of mattress should be chosen to avoid back pain and improve sleep quality?
• U.S. Consumer Product Safety Commission: Bunk Beds Business Guidance
• Product pages on kingsamishfurniture.com (as listed in November 2026)

How we made this guide: we read all 18 mattress pages and 139 bed pages on our site and counted sizes, heights and foundation options, checked standard mattress sizes and the bunk bed rule, read published research on mattresses and back pain, and reviewed mattress questions our team has taken to our builders. Every fact was checked against our product pages.