Inside the window frame or over it on the wall: type what your tape measure says and get the blind size to order, the way the blind makers ask for it, with nothing taken off by you.
Blind to order
35⅛″ × 60⅛″, inside mountthe narrowest width and the longest height · its headrail sticks out of the frame about ¾″
Quick answer: for blinds inside the frame, measure the width at the top, middle and bottom and order the narrowest; measure the height at the left, middle and right and order the longest (the shortest for vertical blinds). Take nothing off: the factory does (Levolor, Bali). For blinds outside, over the frame, add 1½″ each side (3″ for roller shades and vertical blinds) and order the height from the headrail’s spot to the sill.
How to use the blinds size calculator
- Pick where it hangs: inside the window frame, or outside it on the wall or the trim.
- Pick the blind or shade. It changes the depth the frame needs and the overlap outside.
- Inside: measure the frame’s width in three places and its height in three places with a steel tape, to the nearest ⅛″, and the depth at the top. Outside: measure the width you want covered and the height from where the headrail goes to the sill.
- Read the size to order, width × height, and whether the frame is deep enough for that blind.
The rules behind the numbers
Inside mount: the narrowest width, the longest height
Levolor: “Measure inside the window frame horizontally in 3 places to the nearest ⅛ inch: top, middle & bottom. The shortest measurement = your width”, and vertically “in 3 places … left, middle & right. The longest measurement = your height.” Bali’s guides say the same for every horizontal blind and shade. The one exception is Bali’s vertical blinds guide, which records the shortest height, so the vanes clear the sill.
Take nothing off
Levolor: “Do not take deductions from your measurements. For Inside Mount, we will make adjustments to ensure a perfect fit.” Bali: “The manufacturer will take necessary deductions for a perfect fit”, and for cellular shades it names the number: “a ⅜″ deduction off the overall width”. Take a deduction yourself as well and the gap beside the blind doubles.
Outside mount: overlap each side
Bali recommends “1½″ overlap on each side of the window (3″ total) for optimum light control and privacy” on blinds, cellular and Roman shades, and 3″ each side (6″ in all) on roller, solar and vertical blinds; it “makes NO deductions on WIDTH on outside mount installations.” Levolor’s floor is “at least an additional ¾ inch” each side. The brackets need at least 2″ of flat wall or trim above the window (Bali).
How deep the frame must be, by blind
| Blind or shade (Bali) | Partly inside | Flush inside | Outside overlap |
|---|---|---|---|
| 1″ aluminum mini blinds | ¾″ | 1¾″ (with its valance) | 1½″ a side |
| 2″ faux wood blinds, cordless | ¾″ | 3¾″ | 1½″ a side |
| ¾″ cellular shades, cordless | ⅝″ | 2⅝″ | 1½″ a side |
| Roller or solar shades, cordless | 2″ | 2½″ | 3″ a side |
| Roman shades, flat fold, cordless | ½″ | 2⅛″ | 1½″ a side |
| Vertical blinds | 2⅜″ | 2¾″ | 3″ a side |
“Partly inside” is the least depth for the headrail to sit in the frame with its front sticking out; “flush” puts all of it inside. The numbers are from Bali’s own measuring guides; Levolor’s range is “from ½ inch to 3 inches”. Another brand’s product page lists its own.
Three worked examples
Faux wood blinds inside a frame 35¼″, 35⅛″ and 35¼″ wide, 59⅞″ to 60⅛″ tall, 3″ deep. Order 35⅛″ × 60⅛″: the narrowest width, the longest height. The frame is ¾″ short of flush, so the headrail sticks out about ¾″.
A cellular shade inside a 30″ frame that narrows to 29⅞″, 1½″ deep. Order 29⅞″ × 48⅛″. Bali makes it 29½″ wide (⅜″ off), and its headrail sticks out about 1⅛″.
A roller shade outside, over trim 41″ wide, hung 66″ above the sill. Order 47″ × 66″: 3″ past the trim each side. Levolor’s least overlap would make it 42½″.
Common blind measuring mistakes
- Measuring once. A frame can be narrower in the middle than at the top, and windows that look alike differ: “size variances are common” (Bali).
- Taking off a deduction yourself. The factory already does, and the gap doubles.
- Forgetting the depth. Handles and cranks “can interfere with the operation of inside mount treatments” (Bali), and a shallow frame leaves the headrail sticking out.
- A cloth tape. Both makers ask for a steel one; cloth stretches.
- Mixing up width and height. Every maker writes width first: 35⅛ × 60⅛.
Layering curtains over the blinds? The free curtain size calculator gives the panels and rod. Replacing the window first? The window size finder names the size to order, and the free 2D room planner lays out the room around it.
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Blind measuring questions
How to measure for blinds?
Decide first: inside the frame or outside it. Inside, measure the width at the top, middle and bottom and the height at the left, middle and right, to the nearest ⅛″; order the narrowest width and the longest height, with no deductions. Outside, measure the width to cover, add the overlap each side, and measure from the headrail’s spot to the sill.
How to measure windows for blinds?
With a steel tape, inside the frame: three widths, three heights and the depth at the top. The narrowest width and the longest height are the size to order; the depth says whether the blind fits inside (Levolor, Bali).
How to measure for inside mount blinds?
Width inside the frame at the top, middle and bottom: order the narrowest. Height from the top of the frame to the sill at the left, middle and right: order the longest (the shortest for vertical blinds). Do not take anything off: “we will make adjustments to ensure a perfect fit” (Levolor).
How to measure for outside mount blinds?
Measure the width you want covered and add the overlap: 1½″ each side for most blinds and shades, 3″ each side for roller and vertical blinds (Bali). Measure the height from the top of where the headrail goes to the sill, or lower. Outside mounts are made to your exact numbers.
Inside mount vs outside mount blinds: which is better?
Inside shows off the trim and needs a deep enough frame; the maker’s small deduction leaves a thin gap of light each side. Outside hides the gaps, covers a window that is not level and clears cranks and handles, and it makes a window look bigger (Bali’s reasons). Too shallow a frame decides it: outside.
What are standard blind sizes?
Stock blinds come in set widths and lengths; custom blinds are made to your measurement, to the ⅛″ the makers ask for. Inside a frame, a stock blind must not be wider than the narrowest width you measured.