Choose a plan the calculator supports
This walkthrough covers plain face fabric cut as full-width vertical drops and joined for a pencil-pleat curtain plan. Choose one curtain or a balanced pair per window. You can repeat the same plan for up to 20 identical windows. The estimate does not include lining, interlining, heading tape purchases, or fabric-pattern matching.
Work from your actual fabric and tape instructions. All construction allowances in the tool are editable. A sample value is a starting point for a calculation, not a cutting instruction for every project.
Step 1: establish the width to cover
Start with rod or track width. Add the two outer-edge returns and the total center overlap if your plan uses them. Multiply that coverage by the target fullness to obtain the usable flat curtain width you need.
For a balanced pair, each curtain needs half of that target width. Keep the target separate from raw fabric width: the fabric still has to lose material to edges and joins.
Our metric example uses a 200 cm rod, zero returns and overlap, and 2.5× fullness: 200 × 2.5 = 500 cm of target flat width. For two equal curtains, each needs at least 250 cm. The finished curtain length is 220 cm.
Step 2: allow for the joins and finished sides
Subtract the entered selvage removal from both edges of each fabric width. When two widths are joined, the seam takes an allowance from each adjoining edge. The two outer side hems also consume width.
The tool finds the smallest whole number of full-width drops per curtain that still meets the usable-width target after those deductions. For a balanced pair, it uses the same number of drops on each side.
The roll is 140 cm wide. Trimming 1 cm from each selvage leaves 138 cm. Each outer side hem consumes 8 cm in total, and each joined edge needs 1.5 cm. One width leaves 138 − 16 = 122 cm, below the 250 cm target. Two widths leave 2 × 138 − 2 × 1.5 − 2 × 8 = 257 cm per curtain. Use two drops in each curtain, four in the window. Their 514 cm combined flat width gives 514 ÷ 200 = 2.57× actual fullness.
Step 3: calculate one cut length
Add the finished drop, top allowance, bottom allowance, and trimming allowance. The result is the cut length for one vertical drop in this plain-fabric plan.
Enter the total fabric consumed by each allowance. For example, a double turning uses both folds: entering only the depth of one fold would understate the length. Use the method specified by your making instructions.
For this example only, the heading allowance is 10 cm, the bottom hem allowance is 20 cm, and extra trimming is 5 cm. Each full-width drop is cut 220 + 10 + 20 + 5 = 255 cm long. These are editable example totals; side hems and joining seams reduce width, not this cut length.
Step 4: total the drops and round the purchase
Multiply one cut length by the total number of drops across the project. The tool adds your chosen waste percentage, then rounds upward to your chosen purchase increment. A smaller increment may reduce rounding, but it must match how the fabric is sold.
Review the intermediate values before ordering: drops per curtain, cut length, usable width, actual fullness, waste, and purchase rounding. The cut-plan drawing is a schematic; it does not optimize offcuts or confirm fabric direction.
Four drops × 255 cm = 1,020 cm before extra fabric. Add the example 5% allowance: 1,020 + 51 = 1,071 cm. If the shop sells in 50 cm increments, round upward to 22 increments: 1,100 cm, or 11 m. The shop rounding adds 29 cm beyond the extra allowance.
Repeat the plan for three identical windows
All repeated windows must use the same rod width, finished length, arrangement, fabric and allowances. The diagram shows the construction for one window; repeat it for the stated window count. The purchase summary covers the whole project.
Combine the raw cut lengths before adding the extra allowance and shop rounding. Do not multiply an already-rounded single-window purchase by the window count. The actual fullness and finished width per curtain stay the same.
For different window sizes, calculate each size separately. Each calculator keeps only its latest draft on this device, so copy the summary or download a separate backup before starting another plan.
Three windows need 6 curtains and 12 drops. The raw total is 12 × 255 = 3,060 cm. Add 5% (153 cm) to reach 3,213 cm. At 50 cm increments, buy 65 increments: 3,250 cm, or 32.5 m. Rounding adds 37 cm. Multiplying the single-window 11 m by 3 would instead produce 33 m.
Add an optional face-fabric budget
Enter the shop’s unit price and choose whether it is per metre or per yard. That choice is independent of inches or centimetres used for the measurements. Choose a currency label for the estimate; the calculator does not convert currencies or look up fabric prices.
Leave the price blank to skip the budget. The estimate covers face fabric at the final rounded purchase length only, excluding tax, delivery, lining, heading tape and hardware. It is a planning estimate, not a supplier quote.
Using a fictional price of 25 USD per metre, the three-window 32.5 m plan costs 32.5 × 25 = USD 812.50 before tax and delivery. This price is an arithmetic example, not an industry rate. A price per yard must instead be multiplied by the purchased yardage.
Pause when the fabric changes the method
A print with a repeat, a half-drop pattern, a directional design, or fabric intended to run sideways needs additional decisions. Do not treat extra waste alone as a substitute for pattern matching or a different layout.
Confirm the fabric’s usable width and preparation requirements before cutting. This site has not yet had its calculation method independently reviewed by a curtain-making professional; use the breakdown to check the plan with your own making instructions.
References & scope
Methods differ by heading and fabric. These references inform our explanations; they do not imply endorsement or professional review of this site.