Sizing and engineering · Rolling Shutter Guide
How many slats are in a rolling shutter?
It depends on the opening height, slat and box. Roll-A-Shield's formula: clear height + 2 in + the box's actual height, divided by the slat height, rounded up, minus 2. A 48 in tall opening takes 36 slats with the 38 mm slat and a 6.5 in box, or 25 with the 55 mm slat and an 8 in box.
Key facts
- Slats = round up ((clear height + 2 in + actual box height) / slat height) – 2. Roll-A-Shield data
- The factory uses the metric slat heights: 38 mm = 1.496 in, 55 mm = 2.165 in, 63 mm = 2.480 in. Roll-A-Shield data
- Roll-A-Shield's stock 48 x 48 in shutters have 36 slats (38 mm, 6.5 in box) and 25 slats (55 mm, 8 in box), matching the formula. Roll-A-Shield data
- As a rule of thumb a 38 mm curtain has about 8 slats per foot of height, a 55 mm curtain about 5-1/2 and a 63 mm curtain about 5. Roll-A-Shield data
Applies to: Rolling shutter curtains of any make; the formula and table are for Roll-A-Shield 38 mm and 55 mm insulated and 63 mm single-wall shutters.
The number of slats in a rolling shutter curtain is set by its height, not its width. The size of the box goes into the sum as well, so the same opening can take a different count with a different box. This page gives the formula Roll-A-Shield's configurator uses and a table for common heights.
What is the formula?
Roll-A-Shield's configurator counts slats like this:
Slats = round up ((clear height + 2 in + actual box height) / slat height) – 2
- Clear height is the height of the opening itself. The extra 2 in gives the curtain height.
- Actual box height is the real height of the box, slightly more than its nominal size; the box is picked from the slat and the curtain height.
- Slat height is the face height of one slat, in inches.
| Slat | Slat height used | Nominal |
|---|---|---|
| 38 mm insulated | 1.496 in | about 1.5 in |
| 55 mm insulated | 2.165 in | about 2-3/16 in |
| 63 mm single-wall | 2.480 in | about 2.5 in |
Worked example: how many slats for a window four feet tall?
A 48 in tall opening with the 38 mm slat:
- Curtain height: 48 + 2 = 50 in.
- Box: a 50 in curtain on the 38 mm chart takes the 6.5 in box, actually 6.575 in tall.
- Add the box: 50 + 6.575 = 56.575 in.
- Divide by the slat height: 56.575 / 1.496 = 37.8, rounded up to 38.
- Subtract 2: 36 slats.
That is exactly the count on Roll-A-Shield's stock 48 × 48 in 38 mm shutters; the 55 mm stock unit, with an 8 in box, works out at 25 slats the same way.
How many slats for my height?
Counts from the formula, using the box each slat normally gets at that height (55 mm on a 60 mm axle, 63 mm with end retention on every slat):
| Clear height | 38 mm insulated | 55 mm insulated | 63 mm single-wall |
|---|---|---|---|
| 36 in | 28 (6.5 in box) | 20 (8 in box) | 16 (6.5 in box) |
| 48 in | 36 (6.5 in box) | 25 (8 in box) | 22 (7 in box) |
| 60 in | 45 (7 in box) | 31 (8 in box) | 26 (7 in box) |
| 72 in | 53 (8 in box) | 36 (8 in box) | 31 (7 in box) |
| 84 in | 61 (8 in box) | 42 (9 in box) | 36 (8 in box) |
| 96 in | 69 (8 in box) | 48 (9 in box) | 42 (9 in box) |
| 108 in | 77 (8 in box) | 53 (9 in box) | 47 (9 in box) |
| 120 in | 86 (9 in box) | 59 (10 in box) | 51 (9 in box) |
A shutter can end up a slat or so different from the table when its box changes: a very wide curtain whose axle would sag too much moves up one box size, a 55 mm curtain on the larger 70 mm axle uses a slightly different box chart, and a 63 mm curtain with end retention on every other slat does too. The table also ignores size limits; a tall shutter may not be possible in every slat at every width, as why slat choices narrow explains.
Is there a quick rule of thumb?
Yes, for the opening itself: a 38 mm curtain has about 8 slats per foot of height, a 55 mm curtain about 5-1/2 and a 63 mm curtain about 5. The formula's total is a few slats higher, because it adds the 2 in and the box height before dividing.
Why would I need to know the slat count?
Mostly when replacing or matching slats, where the count is a useful check alongside the opening height, the slat and the box. See ordering a replacement slat roll, matching replacement slats and, for a single bent slat, replacing one damaged slat. To check a count or order slats, call (480) 921-0200.
Frequently asked questions
How do I tell which slat my shutter has?
Measure the face of one slat, top to bottom, with the shutter closed. About 1.5 in is a 38 mm slat, about 2-3/16 in a 55 mm slat and about 2.5 in a 63 mm single-wall slat.
Does the width of the shutter change the number of slats?
Not directly; the count comes from the height. Width matters only if it changes the box: a very wide curtain can need the next box size up, which can add a slat.
Are all the slats the same?
Not always. For example, Roll-A-Shield's stock 48 x 48 in 38 mm crank shutter has 33 vented slats and 3 solid ones.
Parts and next step
Need a part or a hand?
Replacement motors, remotes, straps, slats and hardware ship from our Tempe, Arizona factory. Phoenix-area owners can book a service visit; everywhere else, our technicians help by phone. Call (480) 921-0200; the factory answers technical questions for any rolling shutter, not only ours.