Curtain Size Calculator
Measure your window, pick your style, get perfect results
Your Perfect Fit
Curtain Size Calculator
Find the perfect curtain width and length for any window in under a minute. Enter your window measurements below and we'll tell you exactly what size curtains to buy, how high to mount your rod, and how many panels you'll need for a full, tailored look.
Use the Calculator in 4 Quick Steps
- Measure your window width from outside edge to outside edge of the frame (or the trim, if you have it).
- Measure your desired curtain length from where the rod will sit down to your chosen stopping point — sill, apron, floor, or puddle.
- Pick your fullness style — tailored, standard, or luxurious — so we can size the panels for the right amount of gather.
- Hit Calculate. You'll get a rod width, total panel width, individual panel size, and a recommendation for how many panels to buy.
That's it. No math, no returns, no guessing at the store.
Why Curtain Sizing Actually Matters
Most people buy curtains that are too small. It's the single most common decorating mistake in a home, and it's the reason a room can feel "off" even when everything else looks great. Undersized curtains make windows look smaller, ceilings look lower, and the whole space feel a little cramped.
The fix isn't expensive drapes or a designer — it's just knowing the four numbers that matter: rod width, rod height, panel width, and panel length. Get those right, and even budget curtains from a big-box store will look intentional and elevated.
This calculator handles the math. The guide below explains what's happening under the hood so you can make confident choices for every window in your home.
How to Measure Your Window (The Right Way)
Grab a metal tape measure — cloth ones stretch and lie to you — and write your numbers down as you go. Measure in inches; it's how curtains are sold in most markets.
Width. Measure the actual window opening from the inside of one side of the frame to the inside of the other. Then measure again from outside trim to outside trim. You'll use the second number for most calculations, because curtains should extend past the window on both sides.
Height. Measure from the top of the window frame straight down to the sill, then from the sill down to the floor. You'll want both numbers — the first tells you where the window ends, the second tells you where floor-length curtains need to reach.
Ceiling clearance. Measure from the top of the window frame up to the ceiling. This tells you how much room you have to raise the rod, which is the single biggest lever you have for making a room feel taller.
The Width Formula: Fullness Is Everything
A curtain panel that's exactly as wide as your window will look flat, sad, and stretched when closed. Curtains need to gather. That gather is called fullness, and it's expressed as a multiplier of your rod width.
- 1.5× fullness — Tailored. A clean, modern, minimal look. Panels barely ripple. Best for sheers, cafe curtains, or a contemporary aesthetic.
- 2× fullness — Standard. The sweet spot for most homes. Panels have enough gather to look intentional and pleated when drawn closed, but not so much that they feel heavy.
- 2.5× to 3× fullness — Luxurious. Traditional, formal, hotel-quality drapery. Panels feel dense and expensive. Best for bedrooms, formal living rooms, or any space where you want blackout privacy.
The math: Multiply your rod width by your fullness ratio to get the total panel width you need. If your rod is 60 inches wide and you want a standard 2× fullness, you need 120 inches of total panel width — usually two 60-inch panels or three 40-inch panels.
The Length Formula: Where Should Curtains Stop?
There are four traditional stopping points, and the calculator will size to whichever you pick.
Sill length. The bottom hem sits about half an inch above the windowsill. Practical for kitchens, bathrooms, and any window over a countertop or piece of furniture. Casual and unfussy.
Apron length. The hem falls about four inches below the window frame. A tidy middle ground — long enough to feel finished, short enough to keep radiators, benches, or window seats accessible.
Floor length. The hem stops about half an inch above the floor. This is the most versatile choice and the one designers recommend by default. It works in nearly every room and makes ceilings feel taller.
Puddle length. The hem extends 2 to 6 inches past the floor and pools on the ground. Romantic, dramatic, and traditional. Beautiful in bedrooms and formal spaces, but a magnet for dust and pets.
Rod placement changes everything. Mount your rod 4 to 6 inches above the window frame — or all the way up near the ceiling — instead of directly on top of the frame. Add that distance to your length measurement. This one trick makes windows look significantly larger and rooms feel taller, and it costs nothing.
How Wide Should the Rod Be?
The rod should extend 8 to 12 inches past each side of the window frame. This gives your open curtains somewhere to stack, so they clear the glass and let light in during the day. It also makes the window itself look wider.
For a standard 36-inch-wide window, your rod should be 52 to 60 inches long. For a big 60-inch window, aim for 76 to 84 inches. Bay windows, corner windows, and picture windows have their own rules — the calculator handles all of these.
How Many Panels Do You Need?
Most curtains are sold as individual panels, and most panels are 40 to 54 inches wide. To figure out how many to buy:
- Take your total panel width (rod width × fullness).
- Divide by the width of a single panel.
- Round up.
For a 60-inch rod at 2× fullness, you need 120 inches of curtain. Two 54-inch panels give you 108 inches — a bit thin. Three panels give you 162 inches — plenty of gather. When in doubt, size up. You can never have too much curtain.
Common Mistakes to Avoid
Buying panels that are too short. Curtains hemmed above the floor make a room look chopped and unfinished. If you can't find the exact length you need, buy longer and hem — every dry cleaner can do this cheaply.
Mounting the rod too low. If your rod sits right on top of the window frame, you're missing out on the biggest design upgrade available. Push it up.
Buying just one panel per window. A single panel pulled to one side rarely closes properly and always looks skimpy. Buy in pairs, or in threes for wide windows.
Ignoring fullness. Two panels that just barely meet in the middle when closed = flat, sad curtains. Aim for 2× the rod width in fabric.
Forgetting about hardware. Rings, clips, and hooks add 1 to 2 inches of height. Grommet-top curtains lose about the same amount. Factor this into your length measurement.
Frequently Asked Questions
Do I measure the window or the rod? Measure the window first. Use that number to figure out where the rod should go and how long it should be, then measure curtains to the rod.
Can I use the calculator for blinds or shades? No — this calculator is for rod-hung curtains and drapery. Blinds and roller shades are measured inside the frame and follow different rules.
What if my window is unusual — arched, bay, corner? Measure the widest horizontal span and the tallest vertical drop. Then add extra fullness (2.5× minimum) to account for the shape. For bay windows, treat each section as its own window.
Should curtains touch the floor? For most rooms, yes. Floor-length is the safest, most flattering choice. Sill or apron length is fine over radiators, furniture, or in casual spaces like kitchens.
How much extra fabric do I need for a puddle? Add 2 inches for a subtle break, 4 inches for a soft puddle, and 6 inches or more for a dramatic pool.
Ready to Measure?
Scroll back up, plug in your numbers, and let the calculator do the rest. Save the results, take them to the store or the checkout page, and buy with confidence — no more guessing, no more returns, no more curtains that don't quite fit the window.
