A bed does not have to be old or unusual to fall outside a standard mattress size. Imported frames, handmade beds, built in sleeping spaces and furniture made to fit a particular room can all require different dimensions. The All Foam custom foam mattress builder lets you enter rectangular measurements and choose the finished thickness and foam construction instead of forcing the nearest standard size to fit.
The important question is whether you actually need a made to measure mattress. If the frame matches a normal UK size, a standard mattress is usually simpler. If the internal sleeping space is genuinely different, accurate measurements matter more than the name attached to the bed.
What counts as a non standard mattress size?
A non standard mattress is simply one whose finished width or length does not match the standard size required by the frame or sleeping platform.
The standard All Foam mattress dimensions are:
- Single: 90 cm × 190 cm
- Double: 135 cm × 190 cm
- King Size: 150 cm × 198 cm
- Super King: 180 cm × 198 cm
If the actual internal space is different from those measurements, the nearest standard mattress may leave a gap, overhang an edge or fit too tightly.
This is why an odd size mattress should be ordered from measurements rather than from a familiar label such as small double, short king or continental double unless the exact dimensions have been checked.
Common reasons a bed needs a custom size
There are many legitimate reasons for a non standard bed size.
An antique frame may have been built before modern dimensions became common. A handmade timber bed may have been designed around the room rather than a mattress catalogue. A built in platform can use the available wall to wall space. Bunk beds and shorty beds may be deliberately shorter. Imported frames may follow a different sizing system.
Caravans, motorhomes, boats, day beds and guest spaces can also use dimensions chosen for the available area rather than a standard domestic bed.
Measure the frame, not the old mattress label
Start by removing bedding and, where practical, the existing mattress. Measure the space that the new mattress actually needs to occupy.
Record:
- finished width in centimetres
- finished length in centimetres
- available mattress depth
- whether the frame is rectangular
- any fixed rails, lips or obstructions
- access into the room or sleeping area
Measure in more than one place if the frame is older or handmade.
Our foam mattress cut to size guide explains the measuring process in more detail.
Do not copy an old mattress automatically
An old mattress can change shape over time. Edges can compress, covers can stretch and the core may no longer represent the original finished dimensions.
An old mattress can be a useful reference, but compare it with the actual platform or frame before copying its measurements.
This is especially important with antique beds and older frames. Our custom mattress for antique beds guide covers that situation in more detail.
Check whether the shape is truly rectangular
The All Foam builder lets you build your own mattress online for rectangular dimensions. A rectangle needs only width, length and thickness.
A mattress with cut corners, curves, tapers, wheel arch cut outs or other shaped sections needs more information than three measurements can provide. Shaped mattresses require a template, so contact All Foam before ordering.
Do not reduce a shaped mattress to the smallest rectangle simply to make it fit the online builder. That can create gaps in the finished sleeping space.
Custom rectangular sizes can be entered up to 200 cm × 200 cm
For a rectangular custom mattress, the current builder accepts finished width and length in centimetres up to 200 cm × 200 cm.
The dimensions should describe the finished foam size required for the actual space. Check both values carefully before adding the mattress to the basket.
A custom size can also help when the width and length match a standard bed but the required thickness does not.
Choose the thickness after checking the available height
Custom rectangular mattresses use a whole inch thickness from 1 to 10 inches.
Depth changes the available support and comfort construction, finished bed height and layer choices.
Before choosing, check:
- guard rails on bunk or cabin beds
- headboard height
- fitted sheet depth
- surrounding furniture
- access beneath shelves or fixed structures
- how easy the bed needs to be to get in and out of
For a built in space, a mattress that is too deep can cause just as many problems as one that is too wide.
The available layer choices change with thickness
The builder limits the number of foam layers according to the finished mattress depth.
Custom mattresses below 4 inches use one layer. From 4 to 7 inches, the mattress can use one or two layers. At 8, 9 or 10 inches, one, two or three layers are available.
Every active layer is at least 1 inch. The base support layer must be thicker than the upper layers combined, with the specifically permitted 4 inch construction allowing a 2 inch base and 2 inch comfort layer.
These rules keep the support section as the main part of the mattress.
Our foam layer guide explains why the number of layers should follow the total depth rather than being chosen independently.
Choose support foam before thinking about the top feel
A custom foam mattress is built from the base upwards. The support layer is the foundation of the construction and should be chosen before the upper comfort feel.
The builder includes Medium, High, Severe Very Firm, Reflex Medium and Reflex Grey foam grades for suitable support positions. These provide different levels of firmness and recovery.
Memory foam has a narrower role in the builder. It can be chosen only for the upper comfort position when the mattress uses two or three layers, not as a single layer, support base or middle layer.
A made to measure mattress does not need to imitate a standard model
A common mistake is trying to recreate a standard mattress simply because the bed is an unusual size.
Build the mattress around the required dimensions, finished thickness, preferred feel and supporting base. A shallow guest bed may need one layer, while a deeper everyday mattress may suit two or three layers.
Check the bed base before choosing foam grades
Foam needs a level and supportive foundation. A custom mattress cannot correct a damaged or uneven frame.
Inspect slats, platforms and centre supports. Look for bowed timber, broken fixings, unsupported gaps and sections that move under load.
Repair an uneven frame before taking the final mattress measurements.
Bunk beds and shorty beds need extra depth checks
A non standard bunk mattress is not only a width and length problem. The finished mattress height can affect the usable safety rail height above the sleeping surface.
Always follow the bed manufacturer's instructions and maximum mattress depth where provided. Measure the platform itself rather than copying a worn bunk mattress.
Our custom mattress for bunk beds and shorty beds guide covers ladder, rail and drawer clearances in more detail.
Think about covers and bedding before ordering
Standard All Foam mattress configurations come with their fitted cover. A rectangular made to measure order is supplied as the custom foam mattress without a made to measure cover.
If the mattress will be used with an existing cover, measure carefully and consider how the cover seams and fabric tension affect the internal space. Do not measure an empty fabric cover laid flat and assume those dimensions equal the foam core.
Check whether standard fitted sheets will suit the custom width, length and depth.
When a standard mattress is still the better option
Custom sizing is useful when the bed genuinely requires it, but it should not replace a standard mattress unnecessarily.
Choose a standard mattress when:
- the frame accurately matches Single, Double, King Size or Super King dimensions
- the required depth matches the standard product range
- a fitted mattress cover is important
- the bed does not have unusual clearance restrictions
- the nearest standard size is actually the correct size rather than merely close
A non standard mattress measuring checklist
Before placing a custom order, confirm:
- the bed really falls outside the standard UK sizes
- width and length have been measured from the actual sleeping space
- measurements have been checked in more than one place where necessary
- the frame is rectangular if ordering through the online builder
- the finished thickness is a whole inch from 1 to 10
- the selected layer count is allowed for that thickness
- the base support layer remains the main part of the construction
- memory foam, if selected, is used only as the top layer of a two or three layer mattress
- the bed base is level and supportive
- the finished mattress depth works with rails, furniture and bedding
- you understand that custom rectangular mattresses are supplied without a made to measure cover
- shaped mattresses will be discussed with All Foam because a template is required
Final guidance
Non standard mattress sizes are not a problem when the actual dimensions are known. The key is to measure the sleeping space accurately and decide whether the bed needs a standard mattress, a rectangular made to measure foam mattress or a shaped mattress that requires a template.
For an odd size rectangular bed, the All Foam builder lets you choose the width, length, whole inch thickness and foam construction while keeping the support layer as the main part of the mattress. That makes it suitable for many antique frames, built in beds, shorty beds and other spaces that do not match standard UK mattress sizes.
Do not order from the bed name alone. Measure the finished space, check the base, confirm the required depth and then build the mattress around those facts.