Measuring for curtains is straightforward. You measure the rod width, measure the drop from rod to floor, and you're done. The whole thing takes 10-15 minutes per window.

Get the width wrong and light leaks through the sides. Misjudge the length and you're staring at exposed window frames or stepping on fabric.
This guide shows you what to measure and how to avoid common calculation mistakes.

Why Measurements Matter

Short curtains expose window frames. Narrow ones let light leak through. Long ones drag on the floor collecting dust.

Custom curtains can't be returned. A $400 measurement mistake is permanent.

What You'll Need

• A metal tape measure. Fabric ones stretch and sag.
• A sturdy ladder or step stool.
• Your phone to record measurements and take photos. Three months from now you won't remember which number went with which window.
• An extra person helps with large windows—one holds the tape at the top while the other reads the bottom. You can do it alone though.
• A level helps ensure your rod hangs straight. Sloped rods are noticeable and can't be fixed once installed.

Choosing Your Mounting Style First

Decide if you're mounting inside or outside the window frame before measuring anything. This choice changes every number.

Outside mount puts your rod on the wall above and beside the frame. Most people do this. It makes windows look larger, covers the frame completely, and gives you flexibility.

Inside mount fits your rod inside the window frame recess. You see this when someone has beautiful wood frames worth showing off, when layering curtains over blinds, or when the window is recessed deep enough that inside mounting makes sense.

Outside mount works for almost everything. Inside mount only works when your window recess is at least 3 inches deep, or when you want to showcase the frame.

For inside mounts, subtract 1/4 to 1/2 inch from your recess width when ordering the rod. Curtains need clearance to slide without scraping. Your curtains will be less full too, since you're limited to actual window width.

The rest of this guide assumes outside mount since that covers most residential curtains.

Measuring Curtain Width

Measure your rod or plan where it will go

Already have a rod? Measure it end to end, including finials if your curtain hangs outside them.

No rod yet? Start with your window frame width. Standard practice extends the rod 6 to 15 inches beyond the frame on each side. A 36-inch window gets a 48 to 60 inch rod (36 + 6 + 6 minimum, or 36 + 12 + 12 maximum).

Extend 6-12 inches on each side. This gives curtains room to stack when open and makes your window look wider.

You can extend more if you have wall space. Just make sure you won't hit light switches, door frames, or corners.

Mark your planned bracket positions with a pencil. Use a level so marks are at the same height. Measure the distance between marks. That's your rod width.

Account for stack-back before finalizing rod width

Open curtains bunch up. Figure about 20% of panel width as stack-back.

Two 50-inch panels (100 inches total) stack about 10 inches on each side when open—20 inches of your rod covered by fabric even when curtains are "pulled back."

For windows where light matters, plan for stack-back to sit entirely on the wall, not on glass. A 36-inch window expecting 20 inches of stack-back needs a rod extending at least 10 inches on each side (36 + 10 + 10 = 56 inches).

Sliding doors need even more clearance. Budget for stack-back occupying 30% of panel width, and make sure that entire stack sits on the wall so the door can open.

Calculate total curtain width based on fullness

Curtain panels need to be wider than the space they cover so fabric can gather or pleat. Flat panels matching your rod width exactly look stretched tight.

1.5x fullness means total curtain width is 1.5 times rod width. Creates gentle folds. Works well for casual spaces, smaller windows, lighter fabrics, and tighter budgets.

2x fullness means total curtain width is double rod width. Creates luxurious, full gathers with deep folds. Better for formal rooms, larger windows, heavier fabrics, and when you want room-darkening coverage.

Some curtain styles already have fullness built in, some don't.

Pinch pleat (double, triple), goblet pleat, box pleat, and 4-in-1 header styles come pre-pleated. The manufacturer already created the folds. When ordering these, the width you specify is the rod width you want covered. A 100-inch rod needs 100 inches of ordered width. Fullness is built in.

Grommet, back tab, and rod pocket curtains hang as flat panels. You create fullness by using panels wider than your rod. For these styles, multiply rod width by your desired fullness ratio.

Example with a 100-inch rod and 2x fullness:

Grommet curtains: 100 × 2 = 200 inches total

→ Order two 100-inch panels

Pinch pleat curtains: 100 inches total (fullness built in)

→ Order two 50-inch panels

Buying ready-made? You often can't get exact widths. Get as close as possible. Go slightly wider rather than narrower.

Decide on panel quantity and individual widths

Most windows use two panels that part in the middle. Standard for windows and sliding doors where you want to open from the center.

Some situations need a single panel—narrow windows or doors where you want the curtain pulling to one side only.

For two panels, divide total curtain width by two.

Single panels over 100 inches get heavy and awkward to operate. If your calculations suggest a 150-inch single panel, consider two 75-inch panels instead.

Measuring Curtain Length

Determine rod mounting height

Standard placement puts the rod 6 to 10 inches above the window frame. This looks balanced and makes windows appear taller.

Want ceilings to look higher? Mount the rod closer to the ceiling, even just a few inches below. This draws eyes upward. Works well with 9-foot or higher ceilings.

Check for crown molding, vents, or fixtures that might interfere with rod placement.

Mark your planned rod height with a pencil. Use a level to make sure you're marking at the same height across the entire span.

Choose your desired length style

Sill-length curtains end about 1/2 inch above the window sill. Looks neat and tailored, works well for kitchens, uses less fabric so costs less. The downside: exposes everything below the window—radiators, outlets, scratched walls.

Apron-length curtains extend 4 to 6 inches below the sill. Covers the sill and the apron (trim piece below) while still looking intentional. Good middle ground for casual rooms.

Floor-length curtains hang to about 1/2 to 1 inch above the floor. Most common choice for living rooms, dining rooms, and bedrooms. Looks polished, provides good coverage, doesn't drag on the floor collecting dust and pet hair.

Puddle or break style has 2 to 6 inches of extra fabric pooling on the floor. Looks romantic in photos but impractical. Fabric collects dust, gets stepped on, wears out quickly. Skip this unless you're doing a very formal room with little traffic.

Floor-length is the sweet spot for most people.

Measure from the correct starting point

Pinch pleat, goblet pleat (with hooks): Measure from the bottom of the rod ring to your target length. Rings sit about 1-1.5 inches below the rod.

Grommet curtains: Measure from the grommet center on the rod to your target length. Add 3-4 inches to account for the grommet panel above (check manufacturer specs).

Back tab and rod pocket: Measure from the top of the rod to your target length.

Measure at multiple points because floors aren't level

Don't assume your floor is level. Older homes especially can slope by an inch or more across a wide window.

Measure length on the left side, middle, and right side. Write down all three.

Use the shortest measurement as your final length. Better to have extra clearance on one side than fabric dragging on the other.

If your three measurements vary by more than 2 inches, you have a serious slope.

Practical length tips

High-traffic areas should have a solid 1-inch clearance to prevent tripping.

Homes with pets or small children benefit from keeping curtains slightly shorter—keeps fabric away from grabbing hands and curious paws.

Between standard lengths in ready-made curtains? Size up rather than down. A 96-inch curtain you hem to 94 inches looks fine. An 84-inch curtain that should be 86 inches looks obviously short.

Special Window Situations

Bay windows

Bay windows have three or more panels angled outward. You can't treat this as one flat window.

Measure each section separately. Width of the left panel, center panel, and right panel individually. Measure height for each section too.

Decide between a flexible curved rod following the bay angle, or individual rods for each section. Curved rods give continuous coverage but limit how much you can open curtains. Individual rods let you treat each panel as its own window.

Using a curved rod? Measure the actual curved distance, not straight-line distance. Drape your tape along the curve.

For individual rods, measure each window as you would a standard window.

Sliding glass doors

Stack-back matters most for sliding doors. You need clear space when curtains are open for the door to slide.

Measure your door width, then figure out which direction you want the curtain to pull. One-way draw (pulling to one side) is most common.

For one-way draw, plan for stack-back occupying at least 30% of panel width. An 80-inch door with a 160-inch curtain panel (2x fullness) will have about 48 inches of stack-back. You'd need to extend your rod at least 48 inches beyond the door on the stack side.

For length, go floor-length or slightly above (1 inch clearance). Doors open and close constantly, creating air movement that will catch too-long curtains.

Corner windows

Two windows meeting at a corner create an awkward gap if treated separately.

You can run one continuous rod across both windows with a corner connector piece (works best with grommets or rod pockets).

Easier option: use separate rods for each window and let curtains overlap at the corner.

Arched or unusual window shapes

Arched windows, circles, triangles, and other architectural shapes rarely get curtains following the shape. Too expensive and complicated.

Most people curtain just the rectangular portion below the arch. Treat the straight part as a normal window and leave the shaped part uncovered.

If you want to curtain the entire shaped window, you need custom fabrication and probably professional measuring.

Common Measuring Mistakes

Measuring the window frame instead of the rod position

The window frame tells you where the window is. The rod position tells you where the curtain hangs.

A 36-inch window frame might get a 60-inch rod extending 12 inches on each side. Measure the window and order 36 inches of curtain? You'll have 24 inches of bare wall and rod showing.

Measure where the rod actually is or will be, not the window itself.

Forgetting the fullness calculation

People see a 100-inch rod and order 100 inches of grommet panels, then wonder why curtains hang flat.

Grommet, back tab, and rod pocket styles need extra width to create folds. That 100-inch rod needs 150 to 200 inches of actual curtain width.

Pinch pleat and similar pre-pleated styles don't need multiplication because fullness is built in.

Write down what style you're buying before calculating width. Double-check the style category before multiplying anything.

Ignoring how much vertical space the curtain heading uses

Grommet panels have a 3-4 inch decorative panel at the top where grommets sit. This panel sits above the functional curtain length.

Tab tops have fabric loops adding 2-3 inches.

Rod pockets have a sewn channel adding 1-2 inches.

Measure 90 inches from rod to floor and order a 90-inch grommet curtain? The actual fabric bottom hangs at about 86-87 inches.

Check manufacturer specs for how much length the heading consumes. Add that to your floor-to-rod measurement.

Skipping the stack-back calculation

You install beautiful 2x fullness curtains on your 60-inch window with a 60-inch rod. They look amazing closed. Then you open them and discover they cover 20 inches of your window even when "open."

Stack-back isn't optional. Before finalizing rod width, calculate stack-back based on your chosen fullness and panel width.

Recording and Calculating Your Final Numbers

Write down these three numbers:

1. Rod width (the distance your rod covers)
2. Shortest length (from the three points you measured)
3. Curtain style (grommet, pinch pleat, or rod pocket)

Calculating What to Order

For grommet or rod pocket curtains:

• Width: Rod width × 2 (for 2x fullness)
• Length: Your measured length + 3 inches (for grommet panel)
• Panels: Usually 2

Example: 84-inch rod, 95-inch length measurement

• Order: Two grommet panels, 84" wide × 98" long

For pinch pleat curtains:

• Width: Rod width (fullness is built in)
• Length: Your measured length (no addition needed)
• Panels: Usually 2

Example: 72-inch rod, 98.5-inch length measurement

• Order: Two pinch pleat panels, 36" wide × 98.5" long

For multiple windows, take a photo of each window and write the measurements on your phone or a piece of paper.

Work through your first window slowly—record everything, take photos, double-check calculations. By the second window you'll have it down.