How to use the curtain fabric calculator
- Measure the length of the pole or track, and add any returns or overlaps your track has.
- Decide the finished length: for example to the sill, just below the sill, or to the floor.
- Choose the fullness for your heading and the number of panels (2 for a pair).
- Enter the fabric width and the pattern repeat from the fabric label, then check the hem and seam allowances match how you or your maker sew.
- Read the results: widths per panel, cut length per drop, total fabric, and a cutting diagram.
The construction method this calculator uses
The calculator follows a common method for unlined or simply lined curtains made from fabric used “up the roll”:
- Each drop is a piece cut across the full width of the fabric. Drops are sewn together side by side with vertical seams to make a wide enough panel.
- Every panel is made from the same number of widths. With whole widths only, each panel uses 1, 2, 3… full widths. With half widths allowed, one drop can be cut in half lengthways and each half added to a different panel, so a pair of panels can each use 1½ widths from 3 drops.
- Each panel loses the two side hems from its width, and each seam loses the seam allowance on both joined edges.
- The flat width needed for each panel is (track width + returns and overlaps) × fullness ÷ number of panels.
- The cut length of each drop is the finished length + top allowance + bottom hem. With a patterned fabric it is rounded up to a whole number of repeats so that every drop matches, and one extra repeat is added to the total so you can choose where the pattern starts.
Worked example
A pair of curtains for a 200 cm track, finished length 220 cm, at 2× fullness. The fabric is 137 cm wide with a 64 cm repeat. Side hems use 5 cm per edge, seams 1.5 cm per edge, the heading allowance is 15 cm and the bottom hem 20 cm.
- Flat width needed: 200 × 2 = 400 cm in total, so 200 cm per panel.
- One width gives 137 − 2 × 5 = 127 cm, which is too narrow. Two widths give 274 − 10 − 2 × 1.5 = 261 cm, which is enough. So each panel uses 2 widths and the pair needs 4 drops.
- Drop: 220 + 15 + 20 = 255 cm. 255 ÷ 64 = 3.98 repeats, rounded up to 4, so each drop is cut at 256 cm.
- Total: 4 × 256 + 64 (one repeat to position the pattern) = 1,088 cm, or 10.88 m.
Choose Try an example above (with metric selected) to see these figures.
Limitations
- Lining and interlining are not calculated. Work them out separately.
- Specialist headings such as pinch pleats, goblet pleats, wave and some eyelet systems may need a specific fullness, pleat spacing or extra allowances. Enter the fullness and allowances your heading requires; the calculator does not plan pleats or eyelet positions.
- Railroaded fabric (used sideways) is not supported.
- Horizontal pattern matching across seams is not allowed for. Some patterns need extra width to match across joins.
- Fabric shrinkage, pattern placement at the hem, and blinds or valances are not included.
Frequently asked questions
What fullness should I choose?
Fullness is how much wider the flat fabric is than the track. Around 1.5× gives a light, gently gathered look; 2× is a common standard for gathered and pencil-pleat curtains; 2.5× to 3× gives a fuller look and is often recommended for pinch pleats and sheers. Heading tapes and eyelet or wave systems usually state the fullness they need, so check the instructions for the heading you plan to use.
What is the difference between a panel and a fabric width?
A panel is one finished curtain: a pair of curtains is two panels. A fabric width is one full-width piece cut from the roll. Wide panels are made by sewing two or more widths together side by side, so a pair of curtains might need four fabric widths in total.
What are returns and overlaps?
A return is the part of the curtain that wraps from the front of the track back to the wall at each end. An overlap is where two panels cross in the middle on some tracks. If your track has them, measure them and enter the total so they are included before fullness is applied.
Does this include lining?
No. This calculator works out the face fabric only. Lining is usually calculated separately and is often narrower and cut slightly shorter than the face fabric, depending on the method used.
Can I use it for railroaded fabric?
Not reliably. Railroaded fabric is turned sideways so the roll width becomes the curtain drop, which avoids seams. That needs a different calculation based on total curtain width rather than the number of drops.
Why is the total length rounded up when I buy?
Shops usually cut fabric in steps, such as 10 cm or a quarter yard. The calculator shows the exact length and also rounds it up to a practical amount to ask for. Check the shop’s minimum cut and ask for fabric from a single roll or batch when matching patterns.
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