Curtain Rod Size Chart: Length, Diameter & Brackets 2026

How curtain rod size is worked out

The rod length is the window width plus 10 in: 5 in of overhang on each side, so the curtain can stack clear of the glass when it is open. The rod in centimeters is the rod in inches times 2.54, rounded to the nearest whole centimeter. The diameter follows the window width: a window of 30 in or under takes a 5/8 in rod for light or sheer curtains, a window of 31 to 60 in takes a 1 in rod for medium curtains, and a window over 60 in takes a 1 3/8 in rod for heavy or blackout curtains. The brackets follow the rod length: a rod of 48 in or under needs 2 brackets, a rod of 49 to 96 in needs 3 brackets, and a rod over 96 in needs 4. A center support is required when the rod exceeds 48 in, because a long rod sags in the middle under the weight of the curtains.

At the default — a window of 36 in — the rod is 36 + 10 = 46 in, which is 46 × 2.54 = 117 cm, the diameter is 1 in because the window is between 31 and 60 in, and the rod needs 2 brackets with no center support because it is 48 in or shorter.

The worked example, line by line

Setup: window 36 in, reverse rod 48 in.

Line 1 — the rod length. 36 + 10 = 46 in, which is 5 in of overhang on each side.

Line 2 — the rod in centimeters. 46 × 2.54 = 116.84, rounded to 117 cm.

Line 3 — the diameter. The window is 36 in, which is between 31 and 60 in, so the diameter is 1 in.

Line 4 — the brackets. The rod is 46 in, which is 48 in or under, so it needs 2 brackets.

Line 5 — the center support. The rod is 46 in, which does not exceed 48 in, so no center support is needed.

Line 6 — the reverse. A 48 in rod fits a window up to 48 − 10 = 38 in wide, and a 70 in rod fits a window up to 60 in wide.

Every branch, checked

24 in window: the rod is 24 + 10 = 34 in (86 cm), the diameter is 5/8 in because the window is 30 in or under, and it needs 2 brackets with no center support. A small window takes the lightest rod, and two brackets hold it.

60 in window: the rod is 60 + 10 = 70 in (178 cm), the diameter is 1 in because the window is between 31 and 60 in, and it needs 3 brackets with a center support, because the rod exceeds 48 in. A wide window needs the middle bracket or the rod sags.

72 in window: the rod is 72 + 10 = 82 in (208 cm), the diameter is 1 3/8 in because the window is over 60 in, and it needs 3 brackets with a center support. A very wide window takes the thickest rod and the middle bracket.

48 in window: the rod is 48 + 10 = 58 in (147 cm), the diameter is 1 in, and it needs 3 brackets with a center support, because the rod is 58 in, which exceeds 48 in. This is the first window where the middle bracket appears: the window is 48 in, but the rod is not.

30 in window: the rod is 30 + 10 = 40 in (102 cm), the diameter is 5/8 in, and it needs 2 brackets with no center support. A 30 in window is the widest that still takes the light rod.

Reverse — the 48 in rod: a rod of 48 in fits a window up to 48 − 10 = 38 in wide, and a rod of 70 in fits a window up to 60 in wide. If the rod you own is shorter than the window plus 10 in, the curtains will cover the glass when they are open.

What the defaults assume

The model assumes the rod is mounted above the window with the curtains hanging to the sill or the floor: a rod mounted inside the frame, or a rod for a bay window, follows different rules. It assumes the window width is the glass plus the frame, measured across, not the trim. It assumes the diameter follows the window width, which is right for ordinary curtains, but a sheer curtain on a wide window can take a thinner rod, and a blackout curtain on a narrow window needs a thicker one. It leaves out the finials, which add length past the brackets, and the curtain fullness, which decides how wide the curtain itself must be. Rounding convention: lengths are whole inches, centimeters are rounded to the nearest whole centimeter, and all figures are computed from unrounded values, rounded only for display.

Output · formula · meaning

Who uses this

• The homeowner hanging curtains for the first time: they learn a 36 in window needs a 46 in rod — and they learn it is a 1 in rod on 2 brackets, so they buy the right rod the first time and the curtains clear the glass.
• The renter with a rod left by the last tenant: they learn a 48 in rod fits a window up to 38 in wide — so they know whether the rod they own fits the window they have, before they drill a single hole.
• The couple hanging blackout curtains in the bedroom: they learn a 72 in window needs an 82 in rod at 1 3/8 in diameter — so they know the thin rod they almost bought would sag under the heavy curtains.
• The landlord fitting out a wide living-room window: they learn a 60 in window needs a 70 in rod with 3 brackets and a center support — so they know to buy the middle bracket, not just the two ends.

Accuracy & limitations

The math is exact for the numbers you enter: the rod is the window width plus 10 in, the centimeters are the inches times 2.54, and the brackets follow the rod length. What the model cannot do is measure your window for you: measure the glass plus the frame, across, and for a window that follows a bay or a corner, measure each straight run, not the straight-line distance. It assumes the diameter follows the window width, which is right for ordinary curtains, but a sheer curtain on a wide window can take a thinner rod, and a blackout curtain on a narrow window needs a thicker one. It leaves out the finials, which add length past the brackets, and the curtain fullness, which decides how wide the curtain itself must be. For the curtain to go with the rod, see curtain size chart; for the filter in the same room, see air filter size chart.