Curtain Size Calculator

The short answer

Make the rod wider than the window, so the open curtains stack beside the glass: about a sixth of the window’s width past each side, and at least 4 in. Mount it at least 4 to 6 in above the window, or halfway to two-thirds of the way to the ceiling to make the window look taller. Then measure from the top of the rod to where you want the curtains to end, about 0.5 in above the floor for the classic look, and pick the standard length that gets there.

For a 40 in window under a 9 ft ceiling, that’s a 53.3 in rod with its top at 96.5 in, and 96 in panels.

How to measure

1. The window’s width: measure from the outside edge of the trim on one side to the outside edge on the other, or the frame if there’s no trim.
2. The heights: measure from the floor to the top of the trim, and from the floor to the top of the sill.
3. The ceiling: measure from the floor to the ceiling, or to the bottom of any crown molding, where the rod has to stop.
4. Look around the window: a wall, a cabinet or a radiator beside or under it changes how far the curtains can stack or how long they can be.

How to use the calculator

1. Enter the window’s width and heights, and the ceiling height. A ceiling you entered in another tool carries over.
2. Choose the length and the fullness: just above the floor, touching it, breaking on it, puddled, to the sill or below it; and how full you want the curtains when they’re closed.
3. Choose the rod height, toward the ceiling or just above the window, and whether the curtains hang from the rod or from clip rings.
4. Enter the width of one panel from the label.
5. Read the result: the rod’s length and height, the panels to buy and where they end. Every standard length is listed as Fits, Tight or Doesn’t fit, with the rod height or the hem it needs.
6. Save or share it. Copy link keeps your numbers in the address.

How we calculate

If your curtains or rod come with their own measuring notes, follow those first.

• The rod’s length: open curtains need about a third of the window’s width to stack clear of the glass, so the rod reaches about a sixth of the width past each side, and at least 4 in. That also keeps the rod no more than a third wider than the window. The length is bracket to bracket, without the finials. Give a rod over 48 in a center bracket.
• The rod’s height: at least 4 in above the window, and 4 to 6 in up for a rod just above it. Toward the ceiling is halfway to two-thirds of the way up. The top of the rod stays at least 1 in below the ceiling. With no room for that, it goes as high as it can.
• The length: from the top of the rod to where the curtains end, or from the bottom of the rings on clip rings, which add about 3 in. Just above the floor is 0.5 in up, or anywhere from 0.25 to 1 in. A break goes 1 to 2 in past the floor and a puddle 3 to 6 in. To the sill ends 0.5 in above it, and below the sill about 4 to 6 in under it.
• Standard lengths: 63, 84, 95, 96, 108 and 120 in panels, and 24 and 36 in tiers. A length Fits when some rod height in your range ends it where you want. The next longer one is Tight: hem it, or raise the rod when there’s room. A shorter one can’t be let down.
• The panels: the rod’s length times the fullness, divided by one panel’s width and rounded up, then bought in pairs that open from the middle. 2× gives standard fullness, 1.5× a less full look and 3× suits sheers.

Worked examples

Worked example

A 40 in window in a 9 ft room, curtains just above the floor

What we know

• Window: 40 in wide, top 84 in and sill 36 in from the floor
• Ceiling: 108 in
• Curtains: just above the floor, on the rod, 2× fullness, 54 in panels

How it works out

1. Rod: 40 in + 2 × 6.7 in (40 in ÷ 6) = 53.3 in.
2. Rod height: 84 in + ½ to ⅔ of the 24 in to the ceiling = 96 to 100 in.
3. Length: 96 in panels with the rod top at 96.5 in end 0.5 in above the floor.
4. Panels: 53.3 in × 2× ÷ 54 in = 1.98, so two, in one pair.

Two 96 in panels on a 53.3 in rod. Extend the rod 6.7 in past each side of the window, a sixth of its width, so the open curtains stack beside the glass: a 53.3 in rod, bracket to bracket. An adjustable rod sold as 48 to 86 in covers it; over 48 in, give it a center bracket. Mount the rod with its top 96.5 in from the floor, 12.5 in above the window; toward the ceiling is halfway to two-thirds of the way up, 96 to 100 in. 96 in panels then end 0.5 in above the floor. At 2× fullness the curtains add up to 107 in across: two panels 54 in wide, one pair that opens from the middle.

Worked example

A 60 in window in an 8 ft room, the rod just above it, on clip rings

What we know

• Window: 60 in wide, top 80 in and sill 30 in from the floor
• Ceiling: 96 in
• Curtains: with a break on the floor, on clip rings, 2.5× fullness, 54 in panels

How it works out

1. Rod: 60 in + 2 × 10 in (60 in ÷ 6) = 80 in.
2. Rod height: 80 in + 4 to 6 in = 84 to 86 in.
3. Length: 84 in panels with the rod top at 85.5 in and 3 in for the rings end 1.5 in past the floor.
4. Panels: 80 in × 2.5× ÷ 54 in = 3.7, so four, in two pairs.

Four 84 in panels on an 80 in rod. Extend the rod 10 in past each side of the window, a sixth of its width, so the open curtains stack beside the glass: an 80 in rod, bracket to bracket. An adjustable rod sold as 66 to 120 in covers it; over 48 in, give it a center bracket. Mount the rod with its top 85.5 in from the floor, 5.5 in above the window; just above the window is 4 to 6 in up, 84 to 86 in. On clip rings the curtains hang 3 in below the top of the rod, and the length allows for it. 84 in panels then end 1.5 in past the floor. At 2.5× fullness the curtains add up to 200 in across: four panels 54 in wide, two pairs that open from the middle.

Worked example

A 30 in window over a radiator, curtains to the sill

What we know

• Window: 30 in wide, top 72 in and sill 40 in from the floor
• Ceiling: 96 in
• Curtains: at the sill, on the rod, 2× fullness, 54 in panels

How it works out

1. Rod: 30 in + 2 × 5 in (30 in ÷ 6) = 40 in.
2. Rod height: 72 in + 4 to 6 in = 76 to 78 in.
3. Length: 36 in panels with the rod top at 76.5 in end 0.5 in above the sill.
4. Panels: 40 in × 2× ÷ 54 in = 1.48, so two, in one pair.

Two 36 in panels on a 40 in rod. Extend the rod 5 in past each side of the window, a sixth of its width, so the open curtains stack beside the glass: a 40 in rod, bracket to bracket. An adjustable rod sold as 28 to 48 in covers it. Mount the rod with its top 76.5 in from the floor, 4.5 in above the window; just above the window is 4 to 6 in up, 76 to 78 in. 36 in panels then end 0.5 in above the sill. At 2× fullness the curtains add up to 80 in across: two panels 54 in wide, one pair that opens from the middle.

Rod height for each curtain length

Where the top of the rod goes for each standard length, for curtains that hang from the rod. On clip rings, mount it 3 in higher.

Rod and panels by window width

The rod for common window widths, and the panels it takes at 2× fullness.

Fullness and curtain styles

• Flat panels (grommets, rod pockets, tabs) get their fullness from extra width, so give them at least 2× the rod.
• Pleated curtains have the fullness sewn in, so order them to the width they cover.
• Sheers look full at 2.5× to 3× the rod.
• Puddled curtains collect dust and pet hair and tempt pets and toddlers to tug on them. Skip the puddle on curtains you open and close often.

Safety around curtains

• Cords: the CPSC lists window coverings with cords among the top five hidden hazards in the home, and recommends cordless window coverings wherever children live or visit. Setting up a nursery? The nursery checklist generator covers the rest of the room.
• Heaters: keep curtains at least 3 ft from a space heater.
• Radiators and furniture: with a radiator or furniture right under the window, hang the curtains to just above it, not to the floor.

Before you buy

Wash curtains before you hem them, since the fabric can shrink, and remember that linen tends to stretch over time. For a floor that isn’t level, measure the length at both ends of the window and go by the longer one. Layering blinds or shades under the curtains? The blind size calculator gives the size to order inside or outside the frame. Then size the rug for the room with the rug size calculator.