How to Measure a Dock Door for a Seal

What you actually need to measure

Four numbers get you a quote. Everything else we can work out from there.

1. Opening width — inside edge to inside edge of the door frame, measured at the bottom. Not the door leaf, the opening.
2. Opening height — from the dock floor to the underside of the header, at the centre of the opening.
3. Wall space above the opening — how much flat, solid wall you have between the top of the opening and the next obstruction (canopy, light, conduit, track). The head pad has to land on something.
4. Wall space either side — same idea, measured from the edge of the opening out to the first obstruction: downspout, bollard, electrical box, the neighbouring door’s seal.

Measure the opening, not the door

This is the mistake we see most. People measure the door panel, or they measure the outside of the frame. A seal is sized to the opening — the hole the trailer backs up to. If you send us the door leaf dimensions, the pads land in the wrong place and the seal fights the door every time it comes down.

Measure at the bottom of the opening, not the top. Older docks settle, and frames are rarely square after twenty years of trailers hitting them. If the width differs top to bottom by more than an inch, tell us both numbers.

Check your dock height against your trailers

A trailer can legally run up to 13′6″ tall and 8′6″ wide in the United States. What matters for your opening is the difference between that and your dock floor. Subtract your dock height from the tallest trailer you take, and round up to the next foot — that is the door height you need for full access to the trailer.

A 4′ dock taking 13′6″ trailers works out to 9′6″, which means a 10′ door. If your opening is shorter than that, you are not getting the top of the trailer, and no seal will fix it. Worth knowing before you spend money on one.

Common openings run 8′×8′, 9′×9′, 9′×10′ and 10′×10′. Our standard build is 7′4″ wide by 8′ tall, which suits the most common 8′ opening with the pads set inboard of the frame. Everything else we build to spec, and it costs the same to build a custom size as a standard one.

The bumpers matter more than people expect

Your dock bumpers set how far the trailer stops from the wall. The seal has to project far enough past the bumper face that the trailer compresses the foam instead of just touching it. Measure from the wall to the face of your bumpers and send that number too.

If your bumpers are worn down — and on a busy dock they will be — replace them before or at the same time as the seal. A trailer that stops two inches closer than it should will crush new foam past its recovery point in a season. New bumpers are cheap next to a new seal.

Driveway slope

If the approach to your dock slopes down away from the building, the trailer arrives nose-up and the top corners of the opening are the first thing to leak. Tell us the slope, roughly, and which way it runs. On a sloped approach the head pad usually needs more projection than the side pads, and sometimes a seal is not the right product at all — we would rather tell you that than sell you one.

What to send us

Write these down and call or email them in:

• Opening width and height (at the bottom of the opening)
• Clear wall space above and to each side
• Bumper projection, and whether the bumpers are worn
• Dock height, and the tallest trailer you regularly take
• Driveway slope, if any
• How many doors
• A photo of the door, straight on, from about twenty feet back

The photo does more work than you would think. Half the questions we would otherwise have to ask, we can answer by looking at it.

If you are not sure, send what you have

Nobody expects a facilities manager to be a dock seal specialist. Send the numbers you are confident about and a photo, and Dave will tell you what else he needs. We would rather spend ten minutes on the phone than build a seal to a bad measurement.

The five mistakes we see most

1. Measuring the door leaf. The panel is smaller than the opening. Seals are sized to the opening.
2. Measuring only at the top. Frames settle. Measure at the bottom, and tell us if the two differ.
3. Forgetting the obstruction. A downspout, a conduit run or a light fixture eighteen inches off the frame changes the pad width we can use. Look at the wall, not just the hole.
4. Ignoring worn bumpers. Measuring against bumpers that are about to be replaced gives you a seal sized for a dock that will not exist next month.
5. Assuming all your doors match. On a row of six, two are usually different. Measure each one.

Replacing an existing seal

If you are replacing rather than fitting new, measure the opening anyway — do not copy the old unit. There is a fair chance the seal you are replacing was the wrong size, and that is part of why it wore out. Take the four numbers fresh.

Do note what failed, though, and tell us. Foam crushed flat in the middle of the side pads usually means over-compression, which points at bumpers. Wear concentrated on one side points at drivers consistently backing off-centre, which a wider pad or a better guide stripe can help with. Seams opened up means thread, and that is a build quality problem we solve with marine-grade thread and double stitching.

More than one door

Measure each opening separately and label the numbers by door. It takes ten extra minutes and it is the difference between six seals that fit and four that fit. If the doors genuinely are identical, say so and we will build to one spec — but confirm it first.

If you are doing a whole row, tell us that up front. Scheduling six at once is easier for us than six ordered one at a time, and it usually helps the lead time.