Blanket Box Dimensions & Capacity UK: Reference Data for 100 Models

Blanket box capacity is decided by internal dimensions, and internal dimensions are not what is printed on the label. External measurements include the thickness of the sides, the lid and the base, and on an upholstered box they also include the padding, which can remove a surprising amount of usable volume from a piece that looks generous from the outside.

We have not measured a hundred models under controlled conditions and we publish no measured dataset here. What this report provides is the reference framework that makes any blanket box comparable: how to calculate usable capacity, what standard UK bedding actually occupies when folded, and the size bands that suit the positions blanket boxes are typically placed in.

Key findings at a glance

• Usable capacity depends on internal dimensions, and the difference between external and internal volume is largest on upholstered boxes.
• Capacity in litres is the internal length multiplied by the width multiplied by the height in centimetres, divided by one thousand.
• A blanket box placed at the foot of a bed should be no wider than the bed frame, which sets the width by the standard UK mattress sizes.
• Duvet tog rating, not duvet size, is the main determinant of packed volume, because a winter duvet compresses far less than a summer one.
• Hinge type determines whether the full internal volume can actually be used: a lid that does not stay open forces one handed loading.
• Safety restricting hinges or soft close stays are important wherever children have access, and a ventilated or unsealed box is preferable to an airtight one.
• A box used as seating needs a different height from a box used purely for storage, and the two requirements rarely coincide.

The measurement that matters and how to work it out

Start inside the box. Measure the internal length, internal width and internal height from the base to the point where the lid closes, not to the top edge of the sides, because a recessed lid and any hinge hardware reduce the clear height. Multiply the three figures in centimetres and divide by one thousand to give the capacity in litres. This is arithmetic rather than a claim, and it is the only way to compare two boxes fairly.

The gap between external and internal figures varies by construction. A solid timber box with 18mm sides loses 36mm across the width and the same across the depth. A box built from thicker panels loses more. An upholstered ottoman box with a padded interior and a deep padded lid can lose considerably more again, because the padding intrudes on all faces. Two boxes with identical external dimensions can therefore differ substantially in what they hold.

Lid design matters for the same reason. A flat lid that sits on top of the sides preserves the full internal height. A lid with a deep padded underside or an inset panel reduces it. Where a box is bought specifically to hold a winter duvet, that lost height is often the difference between the lid closing and not closing. Comparing the internal figures across the blanket box UK range is more reliable than comparing quoted external sizes.

What bedding actually occupies

UK bedding sizes are standardised, which makes the planning straightforward. A single duvet is 135cm by 200cm, a double is 200cm by 200cm, a king is 225cm by 220cm and a super king is 260cm by 220cm. Pillows are commonly 50cm by 75cm. These are specification figures and they are consistent across the market.

Packed volume, though, is governed by fill and tog rather than by size. A 4.5 tog summer duvet in a microfibre fill compresses to a fraction of its loft. A 13.5 tog winter duvet, and particularly a natural down or feather duvet, resists compression and springs back. A box that comfortably holds two summer duvets may hold only one winter duvet in the same volume. Any planning that treats bedding as a fixed volume by size will underestimate winter storage.

Compression is also a consideration for the bedding rather than the box. Natural fill duvets and wool blankets should not be stored heavily compressed for long periods, as prolonged compression affects loft and, in the case of wool and natural fibres, ventilation matters for the material’s condition. This argues against cramming and in favour of a larger box loosely filled, and it is one reason households frequently end up wanting two smaller boxes rather than one large one. Where the storage need extends beyond bedding, the larger lift up bases in the ottomans UK range solve the problem at the scale of the whole bed.

Placement decides the size band

Blanket boxes go in four places in British homes, and each position sets its own constraints. At the foot of a bed, the width should not exceed the width of the bed frame, which means a box for a double bed should sit within 135cm plus the frame surround, and a box for a king within 150cm plus the surround. A box wider than the bed looks wrong and obstructs the route past the bed.

The second position is the end of a landing or a hallway, where depth is the constraint rather than width. A box projecting more than around 45cm into a landing will interfere with circulation, and in a narrow Victorian hallway even that may be too much. Here a shallow, longer box works better than a deep one, and the lid needs to open without striking a banister or a radiator.

The third is under a window in a bedroom or a bay, where the box doubles as seating. Seat height is the governing dimension, and a comfortable seat height sits in the region of 43cm to 48cm, which is taller than many storage focused boxes. A box at 35cm high is a good store and an uncomfortable seat. The fourth position is at the end of a bath or in a utility area, where moisture makes solid timber or a wipe clean finish preferable to fabric upholstery. The seating question overlaps with the smaller pieces in the modern foot stools UK range, which are often chosen for the same corner.

Reference table: sizing by use

The table below sets out the dimensional requirements for each common use of a blanket box, alongside the standard UK bedding sizes that determine what has to fit. All figures are standard specification dimensions or requirements, not measured survey results.

What this means for UK homes

Measure inside before you buy, or ask for the internal dimensions if they are not published. On an upholstered box the internal figures can be materially smaller than the external ones, and capacity in litres calculated from the internal measurements is the only fair basis for comparison.

Decide whether the box is furniture to sit on or storage to fill, because the two want different heights. If it has to be both, prioritise the seat height at around 43cm to 48cm and accept the capacity that follows, since a box that is the wrong height to sit on will simply never be sat on.

Check the lid mechanism and, where children have access, treat it as the primary specification rather than an accessory. A lid that stays open where it is put allows two handed loading, which is what makes a deep box usable. Leave the box loosely filled rather than packed, particularly with natural fill bedding, and keep it clear of a radiator so that stored textiles are not subject to repeated heating and cooling cycles. Where the storage requirement exceeds one box, a second box or a piece from the clothes storage UK range is a better answer than compressing bedding into a single container.

Methodology

This 2026 report was compiled by the editorial team at Furniture in Fashion. We did not measure one hundred models under test conditions, and no measured dataset, ranking or average dimension derived from a sample is published here. The report is built from standard UK bedding and mattress sizes, standard furniture construction thicknesses, recommended seat heights and circulation clearances, and our editorial assessment as a UK furniture retailer. Capacity figures are not quoted for any product; instead the calculation method is given so that any box can be assessed from its own internal dimensions. No proprietary sales data, customer data or survey fieldwork is included, and no panel provider or academic partner was involved.

Citing this report

Interiors titles and websites are welcome to cite this 2026 reference guide with credit to Furniture in Fashion and a link back to our site. It is an editorial sizing and capacity framework rather than a measured survey of products, and we ask that it is described accordingly. Our storage and bedroom ranges are at Furniture in Fashion.

Frequently asked questions

How do I work out the capacity of a blanket box?

Measure the internal length, width and height in centimetres, multiply them together and divide by one thousand to give the capacity in litres. Measure the height to where the lid closes rather than to the top edge of the sides, and use internal figures rather than the external dimensions quoted on the label.

Will a king size duvet fit in a standard blanket box?

It depends on the fill and tog rating more than the duvet size. A king duvet measures 225cm by 220cm, but a 13.5 tog natural fill duvet resists compression and occupies far more space than a 4.5 tog microfibre one of the same size. Plan for the winter duvet, not the summer one.

What height should a blanket box be if I want to sit on it?

Aim for a seat height of around 43cm to 48cm, which is consistent with comfortable seating generally. Many boxes designed primarily for storage sit lower than this and are uncomfortable to use as a seat, so the height should be decided before the capacity.

Are blanket boxes safe in a child’s bedroom?

Only with the right lid. A box used where children have access should have a restricting hinge or a stay that holds the lid open, should not seal airtight, and should be low enough that a child can reach the base without climbing in. A heavy unsupported lid is the feature to avoid.

How wide should a blanket box at the foot of a bed be?

No wider than the bed frame. For a double with a 135cm by 190cm mattress, keep the box within the frame width, and for a king with a 150cm by 200cm mattress do the same. A box wider than the bed obstructs the route past it and looks out of proportion in the room.