What size garage door bottom seal do you need?
Two numbers, five minutes, one tape measure. Getting either wrong is the most common reason this part gets returned.
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The short answer
You need two measurements, and only two:
- Length: the width of the door, measured across the bottom edge, plus a few inches. Seals are sold in lengths and you trim to fit.
- Bead width: the size of the slot or slots in the retainer track on the bottom of the door. This is the one people get wrong.
Length is forgiving because you cut it. Bead width is not forgiving at all — the seal either slides into the track or it does not.
Measuring the length
Measure the door itself, across the bottom, from outside edge to outside edge. Do not measure the opening, and do not assume your door matches its nominal size.
| Nominal size | Typical door width | Order at least |
|---|---|---|
| Single, 8 ft | About 96 inches | 9 ft of seal |
| Single, 9 ft | About 108 inches | 10 ft of seal |
| Double, 16 ft | About 192 inches | 18 ft of seal |
| Double, 18 ft | About 216 inches | 20 ft of seal |
Buy longer than you measure, every time. Seals are cut to length with a utility knife in about ten seconds, and a seal two inches short is scrap. The extra foot or two costs very little.
Measuring the bead width, which is the part that matters
Open the door so the bottom edge is at a comfortable height, and look at the retainer track from the end. You are looking at either one slot or two.
One slot means a U-shape seal. Measure the width of the opening between the two inward-facing lips. Common sizes are around 3/16 inch and 1/4 inch.
Two parallel slots means a T-end or bead seal. Measure the width of one slot opening, and separately measure the distance between the centers of the two slots — the second number is what determines whether the bulb between them will sit correctly. Common center-to-center spacings are around 1 inch and 1 3/8 inch.
Then photograph the end of the track. A photo against a listing diagram catches mistakes a tape measure does not, and the profile chart is here.
How much gap does the seal actually need to bridge?
The other measurement worth taking, because it decides whether a bottom seal is even the right product. Close the door and measure the gap between the bottom of the seal and the floor at both ends and in the middle.
- Under about 1 inch, and consistent: a standard bottom seal handles it.
- 1 to 2 inches, or consistent but large: look for a deep-bulb or U-shape seal specifically rated for a wider gap.
- Varies by more than about an inch across the width: your floor is uneven and a hanging seal cannot fix it. You want a floor-mounted threshold.
Do not forget the sides and the top
Jamb weatherstrip is sold by the foot and sized by flange width rather than by a bead profile, so it is much simpler to buy. Measure both jambs from floor to header and the header across, add them together, and add a couple of feet.
For a 16-foot double door with an 8-foot opening height that is roughly 8 + 8 + 16 = 32 feet, so buy a 35-foot kit. Doing the sides at the same time as the bottom is the difference between a genuinely sealed opening and a disappointing afternoon.
What to buy, given all that
M-D Building Products
M-D Building Products Garage Door Bottom Seal
Roughly $20-$40 for a door width
The cheapest fix on this entire site, and the one with the biggest effect. A worn bottom seal leaves a gap the width of the door open to the outside all winter, and no amount of heating overcomes an open gap.
Skip it if: Your existing seal is intact and your door still closes flush. Replacing a good seal changes nothing.
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M-D Building Products
M-D Building Products Garage Door Top and Side Weatherstrip
Roughly $25-$50 a kit
The half of the job nobody does. People replace the bottom seal, feel the draft continue, and blame the seal - when the gap is actually along the jambs and the header, where the original strip has shrunk and pulled away.
Skip it if: Your jamb strips are still soft and still touching the door.
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How this was ranked
Every site in this category says it tested twenty of these. We have not tested any, and we say so. What we did instead: built the candidate set from what Amazon actually stocks, compiled the published specifications from each manufacturer’s own pages, did the arithmetic on running cost and on what the thing prevents, and read owner reviews for failure patterns rather than star averages. Every number on this page has a link to where it was published, so you can check the work.
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Frequently asked
What is the standard garage door bottom seal size?
There is no single standard, which is precisely the problem. Common U-shape bead widths are around 3/16 and 1/4 inch; common T-end center-to-center spacings are around 1 and 1 3/8 inch. Length is whatever your door measures plus trim allowance. Measure your retainer rather than assuming.
How much extra garage door seal should I buy?
At least a foot on a single door and two feet on a double. You trim the seal to length with a utility knife, so surplus costs pennies and a short piece is unusable. Buying exactly your measured width is how people end up ordering twice.
Can I use a wider seal to cover a bigger gap?
Up to a point. Seals are sold in different bulb depths, and a deeper bulb bridges a larger gap. What a deeper bulb cannot do is bridge an uneven gap: if the floor slopes, the seal compresses hard at one end and floats at the other. That case needs a floor-mounted threshold instead.
How do I know if my garage door seal needs replacing?
Close the door on a bright day and switch the garage light off. Any daylight along the bottom, the jambs or the header is an unsealed gap. Also press the seal with your thumb: one that has gone hard and does not spring back has stopped conforming to the floor even where it looks like it is touching.