Dock Seals 101: How to Size Them Right and What They Actually Cost
If your dock doors are letting in wind, rain, dust, or the occasional bird, the culprit usually isn't the door itself — it's a missing or undersized dock seal. Dock seals are the foam-filled pads mounted around the door opening that compress against the trailer to close the gap between your building and the vehicle. Get the sizing wrong and you'll have gaps at the corners even with a brand-new seal installed.
Why Projection Size Is the Number That Matters
Every dock seal is rated by two things: the door opening it fits and its "projection" — how far the foam pads stick out from the wall before compression. Projection determines how much variation in trailer height and backing angle the seal can absorb. A shallow 10" projection works fine if your trailer mix is consistent and drivers back in true. If you deal with a wide range of trailer heights, high-cube vans, or drivers who don't always back in square, you need more projection so the pads can still make full contact without gapping at the top or sides.
Undersizing is the most common mistake we see. A facility that installs a 10" projection seal because it's cheaper, then finds a foot of daylight around every third trailer, ends up paying for the seal twice — once for the seal, once for the energy and pest-control losses in the meantime.
What Dock Seals Cost by Size
For a standard 8'x8' door opening, pricing scales directly with projection. A 10" projection seal runs about $1,480, while stepping up to a 15" projection seal is roughly $1,905, and a deep 20" projection seal comes in around $2,048. If your door opening is the larger 8'x9' size, the equivalent range runs from about $1,714 for a 10" projection unit up to roughly $2,286 for an 18" projection unit, with several intermediate sizes in between so you're not overpaying for projection you don't need.
Matching the Seal to Your Traffic
Before you order, measure the actual door opening (not the frame) and take stock of your trailer mix for the last few months. Facilities running mostly standard 53' dry vans with consistent dock height can usually get away with a mid-range 12"–14" projection. Facilities with mixed fleets — straight trucks, refrigerated trailers, high-cube containers — are better served stepping up to 16"–20" projection so the compression range covers the outliers instead of leaving gaps on the odd trailer.
It's also worth checking your dock leveler and bumper setup at the same time. A seal sized correctly for the door opening can still underperform if your bumpers are worn down and letting trailers sit closer or farther from the building than the seal was designed for.
Don't Guess on This One
Dock seals aren't a part you want to reorder in three months because the projection was wrong — they're bolted to the building and sized to the door. If you're not sure which projection fits your trailer mix, send us your door opening dimensions and a rough sense of the trailers you load, and we'll help you match the right size before you order.
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