A curtain fabric calculator estimates the exact yards of material needed using your window width, drop, fullness ratio, and fabric width — skipping guesswork and preventing costly shortages.
One wrong measurement sends you back to the fabric store mid-project. The right number means cutting once, sewing once, and hanging curtains that fit. A curtain fabric calculator — whether you use a free online version or run the math by hand — saves the one thing every sewist values more than money: their time. Below you’ll find the exact formulas, the best free digital tools, and the mistakes that cost yardage.
How To Calculate Curtain Fabric Manually
The manual formula works for any window, any fabric, and any heading style. You need four numbers: the track or pole width, the finished drop (length), the fullness ratio, and the fabric width. Most decorator fabrics come in 54-inch widths, but 46‑ and 60‑inch options are common — always check the bolt label.
The Three-Step Formula
Step 1 — Total Width Required. Multiply the window width by the fullness ratio. Standard ratios are 1.5× for heavy fabrics (velvet, thick linen), 2.0× for average draperies, and 3.0× for sheers. A 90-inch window at 2.0× fullness needs 180 inches of fabric width.
Step 2 — Number of Widths. Divide the total width by the fabric width and round up. For example, 180″ ÷ 54″ = 3.33, so you need four widths of fabric to cover the window without skimping.
Step 3 — Total Yardage. Calculate the cut length by adding 16 inches to the finished drop (that covers the rod pocket and bottom hem). Multiply the cut length by the number of widths, then divide by 36 to get yards. Round up to the nearest half-yard. For a 7-foot drop, the cut length is 84″ + 16″ = 100″. Four widths × 100″ = 400″. 400″ ÷ 36 = 11.11 yards — order 11.5 or 12 yards.
Adjusting For Pattern Repeats
Patterned fabric changes the math. Every panel beyond the first must start at a point that matches the pattern — that means adding one full vertical repeat to the cut length of each additional panel. If the vertical repeat is 27 inches, the second panel’s cut length is 100″ + 27″ = 127″. A simple rule: for large prints, add one extra yard per pair of panels.
Free Online Curtain Fabric Calculators
Digital calculators do the arithmetic and the pattern-repeat adjustment for you. The table below compares the best free options available today.
| Platform | Key Features | Heading Types |
|---|---|---|
| OnlineFabricStore | Custom drapery yardage; inputs for vertical repeat, hem, and fullness | Pencil pleat, pinch pleat, tab top, eyelet |
| Sailrite | Auto-adds 1 inch for hems; custom window curtain estimates | Pencil pleat, pinch pleat, tab top, grommet |
| RM COCO | “Workroom Calculators” for pleated drapery; phone support available | Pleated drapery |
| Morris & Co. | Determines fabric order based on dimensions and heading type | Pencil pleat, pinch pleat, tab top, eyelet |
| Jane Clayton | Works for all heading types; accounts for pattern repeat and fullness | Pencil pleat, pinch pleat, tab top, grommet |
| Sew Helpful | Calculates fabric, lining, and interlining quantities together | Plain and patterned fabric |
All of these tools run in a browser on any device — Windows, macOS, iOS, and Android — and require no sign-up or payment. For a full comparison of top-rated materials for your next project, check out our tested roundup of the best curtain fabrics available.
Double Width Panels And Other Special Cases
Some windows call for double-width panels — each panel uses two widths of fabric sewn together for a fuller look. In that case, multiply the standard yardage by two. If the formula above gave you 11.5 yards for a standard panel, the double-width version needs 23 yards. The same rules for pattern repeats and hem allowance apply to every panel.
Common Curtain Fabric Calculator Mistakes
Five errors cause most shortages and returns. Here is what to check before you cut.
- Rounding down yards. 8.33 yards becomes 8.5 or 9 — never 8. Running short means mismatched dye lots or a second shipping charge.
- Skipping the pattern repeat. Matching patterns at the seam requires the extra length described above. Measure the vertical repeat on the bolt, not the product page.
- Using the wrong fullness ratio. Sheers at 1.5× look anemic; thick velvet at 3× bunches awkwardly. Stick to the ratio that matches the fabric weight.
- Assuming 54-inch widths. Some fabrics measure 46 inches or 60 inches. Verify the actual width on the product listing before you calculate.
- Forgetting the 16-inch hem allowance. The rod pocket, heading, and bottom hem consume real length. Adding only 10 inches leaves the curtains floating above the floor.
Yardage At A Glance: Quick Reference Table
The table below gives ready-made yardage estimates for common window sizes using 54-inch fabric at a 2.0× fullness ratio. Add pattern-repeat adjustments separately.
| Window Width | Finished Drop | Number of Widths | Total Yards (plain fabric) |
|---|---|---|---|
| 48″ | 63″ | 2 | 4.5 |
| 60″ | 84″ | 3 | 8.5 |
| 72″ | 84″ | 3 | 8.5 |
| 90″ | 84″ | 4 | 11.5 |
| 96″ | 96″ | 4 | 12.5 |
| 120″ | 84″ | 5 | 14 |
| 144″ | 108″ | 6 | 20.5 |
Finishing Your Fabric Order
Once you have the yardage number, round it up to the nearest quarter-yard if the calculator allows — precision matters less than having enough. Add one yard per pair of panels for large patterns. Write the final number on the bolt label before you check out, so you can double-check when the fabric arrives. A little planning at this stage means curtains that hang right on the first try.
FAQs
Can I use the same calculator for blackout lining?
Most calculators are designed for the face fabric only. Some, like Sew Helpful, include lining and interlining calculations. For blackout lining, measure your window separately and use the same formula with the lining fabric width — typically 54 inches as well.
Does the formula change for floor-length curtains versus sill-length?
The formula itself stays the same. The only variable that changes is the finished drop. Floor-length curtains usually need an extra inch or two so the fabric barely kisses the floor, while sill-length curtains stop about a quarter-inch above the sill.
What is the most common fabric width for ready-made curtains?
Ready-made curtains are often cut from 54-inch fabric, but the actual width of a single panel depends on the fullness ratio the manufacturer used. Always check the product’s finished width, not just the fabric width, when buying ready-mades.
Do I need to wash the fabric before calculating yardage?
Washing pre-shrinks the fabric. If you plan to wash the finished curtains, pre-wash the yardage before cutting — then calculate using the pre-shrunk length, not the original bolt measurement. Add 5–10 percent to the initial estimate to account for shrinkage.
How do I measure a bay window for curtains?
Measure each section of the bay separately — the front panel and each angled side. Treat every section as its own window for the width and fullness calculation. Add together the yardage for each section to get the total order.
References & Sources
- OnlineFabricStore. “Drapery Yardage Calculator.” Custom calculator with inputs for vertical repeat, hem, and fullness ratio.
- Best Fabric Store. “Yardage Calculator.” Manual calculation guide with rounding and pattern-repeat rules.
- Sailrite. “Window Curtains Fabric Calculator.” Auto-adds 1-inch hems; supports multiple heading types.
- Jane Clayton. “Drapery Fabric Quantity Calculator.” Accounts for pattern repeat and all heading styles.