Sizing and engineering · Rolling Shutter Guide
What is the difference between clear opening, overall size and curtain width on a rolling shutter?
The clear opening is the window or door itself. The overall size is the whole shutter: the clear width plus a guide rail on each side, and the clear height plus the box plus about 2 in. The curtain width is the slat length, a little less than the overall width because the slat ends run inside the rails.
Key facts
- Overall width = clear width + one guide rail each side; Roll-A-Shield adds nothing else, no reveal or allowance. Roll-A-Shield data
- Overall height = clear height + the box's actual height + 2 in. Roll-A-Shield data
- A 48 x 48 in clear opening becomes 52-1/8 x 56-5/8 in overall on a 38 mm shutter (mini rails, 6.5 in box) and 54-3/4 x 58-1/8 in on a 55 mm shutter (standard rails, 8 in box). Roll-A-Shield data
- The overall size, clear opening and guide-rail lengths are each rounded to the nearest 1/8 in. Roll-A-Shield data
- On a recessed mount the factory builds to the overall size you give and takes nothing off; the person measuring subtracts about 1/8 in (up to 1/4 in) so the unit slides in. Roll-A-Shield data
Applies to: Rolling shutters of any make on surface or recessed mounts; the figures are for Roll-A-Shield 38 mm and 55 mm insulated and 63 mm single-wall shutters.
Rolling shutter quotes, drawings and measure sheets use several different sizes for the same shutter, and mixing them up is a common way for an order to go wrong: a clear-opening number entered as an overall size, or the reverse. This page defines each one and shows how Roll-A-Shield gets from one to the other. How to take the measurements is on how to measure for a rolling shutter.
What does each dimension mean?
| Term | What it is |
|---|---|
| Clear opening | The width and height of the window or door itself, inside to inside. Also called the net or inside dimension. |
| Overall width | The full width of the shutter: the clear width plus one guide rail on each side. |
| Overall height | The full height of the shutter: the clear height plus the box plus about 2 in. |
| Curtain height | The clear height plus 2 in: the length of curtain the shutter has to cover and the figure used for its slat count. |
| Curtain width | The length of the slats. It is a little less than the overall width, because the slat ends run inside the guide rails; the factory works out the deduction for each rail type. |
| Guide-rail length | From the sill up to the underside of the box: the clear height plus 2 in. |
| Box size | A nominal size (6.5, 7, 8, 9, 10, 12 in); the real height is slightly more, as in the table below. |
How do you get the overall size from the clear opening?
Add the rails to the width and the box plus 2 in to the height.
- Overall width = clear width + 2 × rail width.
- Overall height = clear height + actual box height + 2 in.
- Both results are rounded to the nearest 1/8 in.
Nothing else goes into the width. Roll-A-Shield does not add a reveal or any extra allowance to the size; how much wall you leave between the window frame and the rail is an installation choice, and installers usually leave about 1/4 to 1/2 in.
Rail width, each side:
| Slat | Rail | Width per side |
|---|---|---|
| 38 mm insulated | Mini | 2.0875 in |
| 38 mm insulated, over 120 in clear width | Wider mini | 2.638 in |
| 55 mm insulated | Standard | 3.346 in |
| 63 mm single-wall | End-retention | 2.944 in |
Box height, nominal and actual:
| Nominal box | Actual height |
|---|---|
| 6.5 in | 6.575 in |
| 7 in | 7.204 in |
| 8 in | 8.15 in |
| 9 in | 9.055 in |
| 10 in | 10.039 in |
| 12 in | 12.008 in |
Which box a shutter gets depends on the slat and the curtain height; see what size box do I need.
What does that look like on a real shutter?
Roll-A-Shield's stock units for a 48 × 48 in clear opening show the arithmetic:
| 38 mm insulated | 55 mm insulated | |
|---|---|---|
| Clear opening | 48 × 48 in | 48 × 48 in |
| Rails | Mini | Standard |
| Box | 6.5 in (6.575 in actual) | 8 in (8.15 in actual) |
| Overall width | 52-1/8 in | 54-3/4 in |
| Overall height | 56-5/8 in | 58-1/8 in |
A larger example: a 96 × 84 in opening with the 55 mm slat gets standard rails and a 9 in box, so it comes out 102-3/4 in wide and 95 in tall overall. All of that surface, not just the opening, has to be clear on the wall for a surface mount.
Where does the extra height go?
Above the opening. The guide rails stand on the sill (or in a U-channel), so nothing is added below; the box and the extra 2 in sit above the top of the opening. The 2 in is there so that when the shutter is fully up the bottom bar stops just under the box and still sits in the rails, leaving the whole opening clear.
If the two sides of the opening are different heights, each rail is made to its own length and the box follows the taller side.
What about a recessed (inside) mount?
On a recessed mount you give the overall size instead, the space the whole shutter must fit into, and the factory builds to that number without taking anything off. So the person measuring makes the allowance: measure the width and height at several points, use the smallest, and subtract about 1/8 in (up to 1/4 in in tight or uneven spots) so the unit slides in without forcing. On a self-install that is you; on a Roll-A-Shield install in metro Phoenix it is the technician.
The clear opening of a recessed shutter is then the overall width less the two rails, and the overall height less the box and the 2 in. The mount types are compared on inside mount or outside mount.
To have the sizes worked out for you, request a quote with your clear-opening sizes and mount type, or call (480) 921-0200.
Frequently asked questions
Does the bottom bar count in the clear opening?
No. The clear opening is the opening only. The bottom bar and the box sit outside it, which is why about 2 in plus the box height is added to get the overall height.
How much wider than my window will the shutter be?
By two rail widths, one each side: 2 × 2.0875 in (about 4-1/8 in) with mini rails on the 38 mm slat, 2 × 3.346 in (about 6-3/4 in) with standard rails on the 55 mm slat, and 2 × 2.944 in (about 5-7/8 in) with end-retention rails on the 63 mm single-wall slat.
Do you round my measurements?
Yes. The factory works out the overall size, the clear opening and the guide-rail lengths in eighths of an inch, each rounded to the nearest 1/8 in, so measure to the nearest 1/8 in.
Should I give you the clear opening or the overall size?
Surface mount: the clear opening, and the factory adds the rails and box. Recessed mount: the overall size of the space the whole shutter must fit, less a small fitting allowance. Label every number so the two are never mixed.
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.