Curtain Size Calculator

This free curtain size calculator works out the pole length, curtain drop and curtain width you need for a window, and matches the result to standard UK ready made curtain sizes, for homeowners and renters in the UK, Ireland and Europe. Enter the window size, pick the length and heading, and it shows the measurements to shop with, in centimetres or inches.

Quick answer: A curtain size calculator adds 15 cm of pole either side of the window, measures the drop from the pole to the sill, 15 cm below it or the floor, and multiplies the pole by the heading fullness. A 120 cm window with a 150 cm pole needs pencil pleat curtains 131 cm wide each.

What Is a Curtain Size Calculator?

A curtain size calculator is a tool that turns window measurements into the pole length, curtain width and curtain drop to buy, so a curtain covers the window fully when closed and clears the glass when open.

The formula in plain words: pole length equals window width plus the overhang on both sides. Curtain drop equals the window height plus the height of the pole above the window, adjusted for the length you want: 1.5 cm short of the sill, 15 cm below the sill, or 1.5 cm short of the floor. Total curtain width equals pole length multiplied by the fullness of the heading, and for a pair each curtain is half of that. The tool then picks the smallest UK ready made width and drop that cover your figures.

How Do You Use the Curtain Size Calculator?

1. Enter the Window width across the recess or the outside of the frame.
2. Enter the Window height to sill and, for floor length curtains, the Sill to floor height.
3. Choose the Curtain length: sill, below sill or floor length.
4. Pick the Heading type. This sets the fullness, for example 1.75 x for pencil pleat.
5. Check the Pole overhang each side and Pole height above window. The defaults are 15 cm for both.
6. Choose Curtains: a pair or a single curtain.
7. Read the curtain size and nearest ready made size, then open “Show the formula and working” to see each measurement.

How Wide Should Curtains Be Compared With the Pole?

Curtains should measure 1.5 to 2.25 times the pole width in total, depending on the heading: about 1.5 x for eyelet, 1.75 x for pencil pleat, 2 x for wave and 2.25 x for pinch pleat. That extra fabric, called fullness, creates the folds when the curtains are closed. A pair of pencil pleat curtains for a 150 cm pole therefore needs 262.5 cm of flat fabric, or about 131 cm per curtain. UK ready made curtains are sold by the flat width of each curtain, so look for 168 cm (66 in) wide curtains in this case, not 117 cm.

How Far Should a Curtain Pole Extend Past the Window?

A curtain pole or track should extend 15 to 20 cm beyond each side of the window. When the curtains are open, the fabric stacks on this extra length instead of covering the glass, so the room gets more daylight. Mount the pole about 15 to 20 cm above the top of the recess or frame; a higher pole makes the window look taller, but it also increases the drop. On a narrow wall, check the pole and its finials fit before you buy.

How Long Should Curtains Be?

Sill length curtains should end about 1.5 cm above the sill, below sill curtains about 15 cm below it, and floor length curtains about 1.5 cm above the floor. Floor length curtains look smartest and keep in more heat, but avoid them if a radiator sits under the window, because they trap warm air behind the fabric. In that case, sill length curtains that finish just above the radiator are the better choice. If you are redecorating at the same time, the paint calculator will tell you how much paint the walls need before the pole goes up.

UK Ready Made Curtain Sizes

The pole limits come from the fullness rule: two curtains of 117 cm give 234 cm of fabric, which divided by 1.75 suits a pole of up to 133 cm. Ready made sizes are usually given in inches first; one inch is exactly 2.54 cm under the international inch definition. Range sizes vary slightly between retailers, so always check the label.

Worked Example: Bedroom Curtains

Example: a bedroom window is 1.2 m wide and 1.2 m from the top of the recess to the sill, with 0.9 m from the sill to the floor. The plan is floor length pencil pleat curtains as a pair, with the pole 15 cm above the window and 15 cm past each side.

• Pole: 120 cm + 2 x 15 cm = 150 cm.
• Drop: 120 cm + 15 cm + 90 cm, minus 1.5 cm clearance = 223.5 cm.
• Curtain width: 150 cm x 1.75 = 262.5 cm, so 131.3 cm per curtain.
• Nearest ready made size: 66 in (168 cm) wide x 90 in (228 cm) drop, 4.5 cm longer than needed.

You can take up the hem by 4.5 cm, or raise the pole 4.5 cm so the curtains still clear the floor. If you later want a blind in the recess as well, the same width measurements work for both.

Measure with a steel tape rather than a fabric one, and write every figure in centimetres. Older windows are rarely square, so measure the drop on the left, centre and right and use the shortest for sill length curtains. For floor length curtains, measure to the floor at several points too, because floors often slope. If the pole is already fitted, measure the drop from the bottom of the rings for pencil pleat curtains, and from the top of the pole for eyelet curtains, then enter the pole height above window as 0 and the drop you measured as the window height.

Lined and thermal curtains add warmth and block light, which matters in bedrooms. They are heavier than unlined curtains, so on a wide window choose a pole or track with a centre support bracket. For more room planning tools, browse our home calculators.

Curtain Size Calculator FAQs

Checked October 2026. Sources: Blinds Direct, How to Measure for Curtains (fullness by heading, overhang, drop clearances), Dunelm, Curtain Help and Advice Hub (ready made widths and drops, pole height), Wikipedia, Inch.