Curtain Size Calculator
Work out the right rod length, panel width, and drop length for your window — including fullness, header allowance, and hem.
Inputs
1.5× tailored · 2× standard · 2.5–3× sheer/luxe
Window & curtain preview (to scale)
Floor length · 2 panelsYour estimate
About Curtain Size Calculator
The Curtain Size Calculator helps you figure out exactly how wide and how long your curtain panels should be — including the fullness ratio that gives curtains their gathered look, the header allowance for whichever top style you're using, and the hem allowance on the bottom and sides.
It's useful for two audiences. If you're buying ready-made panels, the "finished width" and "panel drop" tell you what size to look for in stores. If you're sewing your own, the "per-panel cut size" gives you the exact fabric rectangle to cut, and the "Fabric total" gives the bulk amount to buy.
How to Use Curtain Size Calculator
- 1 Pick your unit. Inches or centimetres — all inputs and outputs follow the choice.
- 2 Measure the window. Use a steel tape across the inside of the trim. Type the width and height of the window opening.
- 3 Set the mounting. "Rod above window" is how high above the trim you'll fix the brackets (6" looks tailored, higher feels grand). "Side extension" is how far the rod extends past each side — 6" lets two panels stack off-window when fully open.
- 4 Choose a length style. Sill / Below sill stop at or below the window. Floor / Puddle ask for the window-bottom-to-floor distance so the drop is correct. Custom lets you type the rod-to-bottom drop directly.
- 5 Pick panels, fullness, and header. 2 panels is standard (a pair). Fullness 2× is the standard gathered look; 2.5–3× for sheers and a more luxurious draped feel. Pick the header type that matches what you'll buy or sew — it adds the right amount to the cut length.
- 6 Read the estimate. Rod length is what to install. Panel width × Panel drop is the finished size of each curtain panel — that's what to shop for. Per-panel cut size (under the dividers) is what to cut from a fabric bolt.
Frequently Asked Questions
What fullness ratio should I use? ▾
1.5× gives a tailored, mostly-flat look — fine for blackout liners and structured pinch pleats. 2× is the standard "gathered curtain" look most people expect. 2.5–3× is what you want for sheers and full-bodied drapes — the extra fabric creates the soft cascade. If in doubt, use 2× for blackout and 2.5× for sheer.
How high above the window should I mount the rod? ▾
The "high and wide" rule looks best in most rooms: rod 4–8" above the window trim, extending 6–12" past each side. This makes the window appear larger and lets the open panels sit off the glass for maximum light. Going higher (12"+) or all the way to the ceiling exaggerates the ceiling height — great in rooms with low ceilings.
Which length style is right for my room? ▾
Sill or below-sill works for kitchen and bathroom windows where the curtain would block counters or radiators below. Floor length is the most flattering for living rooms and bedrooms — aim for ½" above the floor so the panels don't drag. Puddle (1–6" pooling on the floor) is a luxurious, formal look, but harder to clean and not pet-friendly. Custom lets you type your own drop if you want a unique length.
What is the header allowance? ▾
The header is the top of the curtain panel — the part that interacts with the rod. Different headers need different amounts of extra fabric on top: a rod-pocket needs enough to fold over and sew a channel (about 4"), a pinch pleat needs deeper folded fabric for the pleats (about 6"), grommets only need ~1.5". The calculator adds this to the cut length automatically based on your header pick.
What hem allowance is typical? ▾
Bottom hem: 4" double-fold (so cut 4" extra). Side hems: 1" double-fold each side = 2" extra per side = 4" total for both sides. These are the defaults filled in for you. Lighter sheers can use 2" bottom and 1" side. Lined formal drapes sometimes use 5–6" weighted bottom hems for a heavier hang.
How do I read "Per-panel cut size"? ▾
This is the size of the fabric rectangle to cut from the bolt for one panel. Multiply by the number of panels to get total fabric. Make sure your fabric bolt is at least as wide as the panel cut width — if it's narrower, you'll need to piece widths (and add an extra ~1" per seam). 54" upholstery fabric is the standard for curtains.
Is my data saved or sent anywhere? ▾
No. Everything runs in your browser. Your window dimensions and preferences never leave your device and nothing is stored on a server.