How deep should a window seat be?

450–500mm to sit on properly with your back against the window. If you want to curl up and read, 600–700mm — but that is a substantially larger piece of furniture and it intrudes further into the room.

Can I build a window seat over a radiator?

Boxing in a radiator reduces its heat output, sometimes significantly. A ventilated design with a grille front helps but does not fully solve it. If the radiator is a primary heat source for the room, relocating it or choosing a different wall is usually better.

Drawers or a lift-lid seat?

Drawers, in almost every case. A lift lid requires moving the cushion and anyone sitting there, which means it gets used for genuinely seasonal storage and nothing else. Drawers get used weekly.

Design

Window Seat Ideas

Updated July 25, 20262 min read

The short answer

Most window seats are built too shallow to sit on properly. You need 450–500mm of depth to sit comfortably with your back against the window, and 430–460mm of height. Below those numbers you get an attractive ledge that nobody uses.

Working dimensions

Working dimensions
Element	Dimension	Note
Seat height (with cushion)	430–460mm	Chair height. Include cushion thickness in the calculation.
Seat depth, sitting sideways	450–500mm	Minimum to sit properly with back supported.
Seat depth, lounging	600–700mm	For curling up with a book — a different piece of furniture.
Length	900mm min.	Below that it is a chair, not a seat.
Storage depth below	350–450mm	Drawers or a lift lid.
Clearance below window sill	150mm+	Cushion should not hit the sill.

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Practical considerations

Drawers beat a lift lid: A lift-lid seat means moving the cushion and anyone sitting on it. Drawers pulling out from the front get used far more.
Radiators complicate things: Boxing in a radiator reduces its output. If there is one under the window, it needs a ventilated design or relocation.
Windows are cold surfaces: In a Calgary winter, sitting against single or older glazing is unpleasant. A cushioned back or a slightly forward seat position helps.
Condensation runs down glass: Which lands on your seat top. Specify a finish that tolerates it, and consider a small drainage gap at the back.
Bay windows are a joinery job: The angled returns make a bay seat considerably more work than a straight one.
It becomes a landing surface: Whatever you intend, a window seat collects bags and post. Plan for it rather than being annoyed by it.

Answers

Frequently asked questions

How deep should a window seat be?: 450–500mm to sit on properly with your back against the window. If you want to curl up and read, 600–700mm — but that is a substantially larger piece of furniture and it intrudes further into the room.
Can I build a window seat over a radiator?: Boxing in a radiator reduces its heat output, sometimes significantly. A ventilated design with a grille front helps but does not fully solve it. If the radiator is a primary heat source for the room, relocating it or choosing a different wall is usually better.
Drawers or a lift-lid seat?: Drawers, in almost every case. A lift lid requires moving the cushion and anyone sitting there, which means it gets used for genuinely seasonal storage and nothing else. Drawers get used weekly.

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