★ CONSTRUCTION · HOME · WINDOWS
A 36 in window takes a 35.5 in blind inside mount, or a 40 in blind outside mount. Inside mount the blind is the window width minus 0.5 in, outside mount it is the window width plus 4 in. Enter your window size and mount to get the exact blind size, in inches and centimetres.
A blind is sized by its mount: an inside mount sits in the window frame, so it is narrower than the window, and an outside mount sits on the wall around the frame, so it is wider. This chart lists the blind size for the seven window widths people buy most, from 24 to 84 inches, and the lookup works out the blind size and the brackets for your window, so the number you get is the number to order.
A blind is sized by its mount. For an inside mount the blind sits in the window frame, so the blind width is the window width minus 0.5 in, which leaves a quarter inch of clearance on each side, and the blind height is the window height. For an outside mount the blind sits on the wall around the frame, so the blind width is the window width plus 4 in, which covers 2 in of wall on each side, and the blind height is the window height plus 4 in. The brackets are 2 for a blind up to 48 in wide, and 3 for a blind from 49 to 84 in wide, because a wide blind needs a centre support.
At the defaults — 36 in wide, 48 in high, inside mount — the blind is 36 − 0.5 = 35.5 in wide and 48 in high, which is 35.5 × 2.54 = 90.17 cm by 48 × 2.54 = 121.92 cm, with 2 brackets. Outside mount, the same window takes 36 + 4 = 40 in wide and 48 + 4 = 52 in high, which is 101.60 cm by 132.08 cm, also with 2 brackets.
| Window width | Inside mount blind | Outside mount blind | Brackets |
|---|---|---|---|
| 24 in | 23.50 in | 28.00 in | 2 |
| 30 in | 29.50 in | 34.00 in | 2 |
| 36 in | 35.50 in | 40.00 in | 2 |
| 48 in | 47.50 in | 52.00 in | 2 / 3 |
| 60 in | 59.50 in | 64.00 in | 3 |
| 72 in | 71.50 in | 76.00 in | 3 |
| 84 in | 83.50 in | 88.00 in | 3 |
This is a size chart, and it is explicitly not a fitting guide for every window: it does not say how to fit a blind in a bay window, an arched window or a window with a crank handle in the way, and it does not say which headrail a wide blind needs. A window wider than 84 in takes two blinds side by side, because a single blind wider than 84 in sags and is hard to lift. Measure the window in three places and use the smallest width, because a window that is not square needs the smallest measure.
Setup: 36 in wide, 48 in high, inside mount.
Line 1 — the blind width. 36 − 0.5 = 35.5 in.
Line 2 — the blind height. The height is the window height: 48 in.
Line 3 — the size in centimetres. 35.5 × 2.54 = 90.17 cm by 48 × 2.54 = 121.92 cm.
Line 4 — the brackets. The blind is 35.5 in wide, which is 48 in or under, so it needs 2 brackets.
Line 5 — the outside mount. The same window outside mount takes 36 + 4 = 40 in wide and 48 + 4 = 52 in high, which is 101.60 cm by 132.08 cm, with 2 brackets.
24 in wide: the blind is 24 − 0.5 = 23.5 in, with 2 brackets. A narrow window takes a narrow blind, and the 0.5 in clearance is the same at every width.
60 in wide: the blind is 60 − 0.5 = 59.5 in, with 3 brackets. At 59.5 in the blind is wider than 48 in, so it needs a centre support, which is the third bracket.
Outside mount, 36 in: the blind is 36 + 4 = 40 in wide and 48 + 4 = 52 in high, with 2 brackets. Outside mount adds 4 in to the width and 4 in to the height, so the blind covers the frame and 2 in of wall on each side.
Height 60 in (36 in wide, inside): the blind is 35.5 in wide and 60 in high. The height does not change the width, and the brackets stay at 2, because the brackets follow the width.
48 in wide: the blind is 48 − 0.5 = 47.5 in, with 2 brackets. At 47.5 in the blind is still 48 in or under, so it needs no centre support. Outside mount the same window takes a 52 in blind, which is over 48 in, so it needs 3 brackets — the table shows 2 / 3 for this row.
72 in wide: the blind is 72 − 0.5 = 71.5 in, with 3 brackets. A wide blind sags without a centre support, which is why the third bracket appears above 48 in.
30 in wide: the blind is 30 − 0.5 = 29.5 in, with 2 brackets.
84 in wide: the blind is 84 − 0.5 = 83.5 in, with 3 brackets. This is the widest single blind in the chart: wider than 84 in, order two blinds side by side.
Reverse — blind to window: a 35.5 in blind fits a 36 in window inside mount, a 40 in blind fits a 36 in window outside mount, a 47.5 in blind fits a 48 in window, and a 59.5 in blind fits a 60 in window. Measure the blind you have, and the window follows, because the window is the blind plus 0.5 in inside mount, or the blind minus 4 in outside mount.
The model assumes a square window with a flat frame, measured inside the frame for an inside mount and across the frame for an outside mount. It assumes 0.5 in of clearance for an inside mount, 4 in of overlap for an outside mount, and a centre support above 48 in of blind width. It leaves out the headrail depth, the valance and the cord length, which are priced separately, and it does not cover bay windows, arched windows or windows with a crank handle in the way. Rounding convention: sizes to 2 decimals, centimetres to 2 decimals, and all figures are computed from unrounded values, rounded only for display.
| Output | Formula | What it means |
|---|---|---|
| Blind width (inside) | window width − 0.5 in | 35.50 in. |
| Blind height (inside) | window height | 48.00 in. |
| Blind size in cm | inches × 2.54 | 90.17 cm × 121.92 cm. |
| Brackets | blind width ≤ 48 in → 2, else 3 | 2. |
| 24 in wide | same model, 24 in | 23.50 in blind, 2 brackets. |
| 60 in wide | same model, 60 in | 59.50 in blind, 3 brackets. |
| Outside mount, 36 in | window + 4 in | 40.00 in × 52.00 in blind, 2 brackets. |
| Height 60 in | same model, 60 in high | 35.50 in × 60.00 in blind. |
| 48 in wide | same model, 48 in | 47.50 in blind, 2 brackets. |
| 72 in wide | same model, 72 in | 71.50 in blind, 3 brackets. |
| 30 in wide | same model, 30 in | 29.50 in blind, 2 brackets. |
| 84 in wide | same model, 84 in | 83.50 in blind, 3 brackets. |
| Reverse: 35.5 in blind (inside) | blind + 0.5 in | 36.00 in window. |
| Reverse: 40 in blind (outside) | blind − 4 in | 36.00 in window. |
| Reverse: 47.5 in blind | blind + 0.5 in | 48.00 in window. |
| Reverse: 59.5 in blind | blind + 0.5 in | 60.00 in window. |
The math is exact for the numbers you enter: the inside blind is the window width minus 0.5 in, the outside blind is the window width plus 4 in, the height follows the same rule, and the brackets are 2 up to 48 in and 3 above it. What the model cannot do is measure your window for you: measure the width in three places and use the smallest, because a window that is not square needs the smallest measure, and check the depth of the frame, because a shallow frame may not hold an inside mount. It assumes a square window with a flat frame, and it leaves out the headrail depth, the valance and the cord length. It is explicitly not a fitting guide for bay windows, arched windows or windows with a crank handle in the way. For the curtain rod, see curtain rod size chart; for the air filter, see air filter size chart.
Bright Side Kit. "Blind Size Chart: What Size Blinds for My Window? 2026." https://brightoolbox.com/blind-size-chart/ Accessed October 25, 2026.Inside mount for a clean look, outside mount to cover the frame. Inside mount sits in the frame, so a 36 in window takes a 35.50 in blind, and it shows the trim. Outside mount sits on the wall, so the same window takes a 40.00 in by 52.00 in blind, and it covers the frame and 2 in of wall on each side. Outside mount is the answer when the frame is too shallow for an inside mount.
For clearance. A blind that is exactly the width of the frame binds on the sides and will not move. Subtracting 0.5 in leaves a quarter inch on each side, so the blind slides freely. A 36 in window takes a 35.50 in blind, and a 48 in window takes a 47.50 in blind, for the same reason.
Above 48 in of blind width. A blind up to 48 in wide needs 2 brackets, one on each end, and a blind from 49 to 84 in wide needs 3 brackets, with the third in the centre. A 60 in window takes a 59.50 in blind with 3 brackets, and a 48 in window takes a 47.50 in blind with 2 brackets.
Measure in three places and use the smallest width. Measure the width at the top, the middle and the bottom of the frame, and use the smallest of the three, because a window that is wider at the top than the bottom needs the blind to fit the narrowest part. A 36 in window that is 35.75 in at the bottom takes a 35.25 in blind inside mount.
Measure the glass, not the door. A door blind mounts on the door itself, so measure the width of the glass plus the frame around it, and use the outside mount rule: the blind is the width plus 4 in. A 24 in glass panel takes a 28 in blind outside mount, and the blind needs a hold-down bracket at the bottom so it does not swing when the door opens.
Order two blinds side by side. A single blind wider than 84 in sags in the middle and is hard to lift, so the chart stops at 84 in, which takes an 83.50 in blind. A 100 in window takes two 49.50 in blinds side by side, each inside mount, which is two blinds of 50 in window width each.
Multiply the inches by 2.54. A 35.50 in blind is 35.5 times 2.54, which is 90.17 cm, and a 48 in blind is 48 times 2.54, which is 121.92 cm. A 40 in blind is 101.60 cm, and a 52 in blind is 132.08 cm.
The mount. Inside mount the blind is narrower than the window: a 36 in window takes a 35.50 in blind. Outside mount the blind is wider than the window: the same 36 in window takes a 40.00 in blind. The blind width is the number to order, and the window width is the number to measure.