Gaps around doors and windows let warm air out in winter and hot, humid air in during summer. Weatherstripping is one of the cheapest energy upgrades and a classic weekend project. This calculator tells you how much to buy.
Doors
An exterior door needs weatherstripping on both sides and across the top of the frame:
per door = 2 × height + width
The bottom gap is sealed with a door sweep or a new threshold, counted separately.
A 36 × 80 in door: 2 × 80 + 36 = 196 in, about 16.3 ft.
Windows
For casement and awning windows, seal the whole perimeter of each sash:
per window = 2 × (width + height)
A 36 × 48 in window: 2 × 84 = 168 in, 14 ft. Double-hung windows also need a strip on the meeting rail where the two sashes overlap, and sliding windows on the interlocking stiles; add a little extra.
Example
Two doors and eight windows: 2 × 196 + 8 × 168 = 1,736 in, or 145 ft. With 10% extra for corners and mistakes: 159 ft, so 10 rolls of 17 ft and 2 door sweeps.
Which type to choose
| Type | Best for | Durability |
|---|---|---|
| Adhesive foam tape | Irregular gaps, windows that do not open often | 1 to 3 years |
| V-strip (tension seal) | Sides of double-hung and sliding sashes, door jambs | Long-lasting |
| Rubber or silicone tubular gasket | Doors, larger gaps | Several years |
| Felt | Low cost, low traffic | Short |
| Door sweep or threshold | The gap under a door | Several years |
Match the thickness to the gap: the strip should compress when the door or window closes, without making it hard to latch.
Installation tips
- Clean the surface and let it dry; adhesive strips fail on dirty or cold surfaces, so work above about 50 °F.
- Measure each run and cut with a little extra; trim at the corners.
- Test by closing the door on a sheet of paper: if it slides out easily, the seal is not tight.
- On a windy day, a lit incense stick near the frame shows where air still leaks.
Combine weatherstripping with caulk on the fixed joints around trim, where frames meet the wall, and with foam gaskets behind outlet covers on exterior walls.