A window seat is a low cupboard with a cushion on top, but it's sat on, so it has to be the right height, deep enough to be comfortable, and strong enough for an adult. Get those right and the storage underneath is a bonus.
Height
A comfortable seat is about 450 mm off the floor, the height of a dining chair, measured to the top of the cushion. Take the cushion's thickness off to get the height of the seat itself: with a 75 mm cushion, build the top at about 375 to 400 mm.
Check the window first: the seat and cushion must sit below the sill or window board, with room to open the window and reach its handle.
Depth
- 400 to 450 mm is enough to sit upright.
- 500 to 600 mm is better for leaning back against cushions on the wall.
- 700 mm or more lets someone lie down or sit sideways with their legs up, which is what most people really want in a bay.
Strength
Build the carcass from 18 mm board and support the top across its width at least every 600 mm, with dividers, a frame or bearers, so it doesn't bounce or sag when two people sit on it. A lift-up lid needs a strong frame round it too.
Storage underneath
- Drawers are the easiest to use: nothing has to be moved to get in. The drawer box calculator gives each part's size and the runner length.
- Cupboard doors at the front are cheaper and suit bulky things.
- A lift-up lid uses all the space but the cushion has to come off each time; fit lid stays so it can't drop on fingers.
Radiators under the window
A radiator under the window is common, and boxing it in tight wastes its heat. Either move the radiator, or build that part of the seat with a grille or slotted front and an open gap at the back of the top, so warm air can rise. Keep the valves where they can be reached.
Bay windows
A bay is the best place for a window seat and the hardest to fit, because the walls meet at angles. Measure each wall of the bay and the angle between them, build a unit for each wall, and join the tops with mitres where the walls meet. Scribe the ends to the walls.
Plan it in JoinerKit
In JoinerKit, draw the room to its shape, bay and all, with each wall at its real angle. Add cupboard units at seat height along the window walls, with drawers or doors, and see it in 3D with the window above. It works out the cutting list, sheet layouts and price, and says if the drawers don't fit.
Questions
How high should a window seat be?
About 450 mm to the top of the cushion, like a dining chair. Take the cushion's thickness off for the seat itself: about 375 to 400 mm with a 75 mm cushion.
How deep should a window seat be?
400 to 450 mm to sit upright, 500 to 600 mm to lean back, and 700 mm or more to stretch out.
Can I build a window seat over a radiator?
Yes, if the front over the radiator has a grille or slots and the top is open at the back, so warm air can get out. Keep its valves reachable, or move the radiator.