What is the standard fullness ratio for curtains?

The standard fullness ratio for curtains is 2.0, which gives a balanced gather. Lightweight fabrics can use 1.5, while heavy fabrics like velvet or blackout linings often use 2.5 for a fuller look.

How much extra fabric should I buy for patterned curtains?

For patterned curtains, add the pattern repeat length to the cut length per width. For example, if the pattern repeats every 64 cm and the calculator shows a cut length of 205 cm, round up to 256 cm (4 × 64 cm) to match the pattern across widths.

Can I use the calculator for blackout curtains?

Yes, the calculator works for blackout curtains. Use a fullness ratio of 2.0–2.5 to ensure full coverage, and add a lining if needed. The calculator’s 10% margin helps cover any extra fabric required for lining.

What is the typical hem allowance for curtains?

The typical hem allowance for curtains is 20–25 cm (8–10 inches), which covers the top heading and bottom hem. For short curtains or café curtains, you can reduce this to 10–15 cm.

How do I calculate fabric for a bay window?

For a bay window, measure each section of the pole separately and use the calculator for each section. Sum the total fabric required for all sections. The calculator’s live results make it easy to add up the totals.

Does the calculator work for Roman blinds?

No, the calculator is designed for curtains, not Roman blinds. Roman blinds require different calculations based on the blind’s width, drop, and fold depth. Use a dedicated Roman blind calculator for accurate results.

Calculate Curtain Fabric in Minutes with This Free Tool

To calculate curtain fabric, multiply the pole width by the fullness ratio, divide by the fabric width to find how many widths you need, then add hem and heading allowances to the drop for the cut length per width. A free online Curtain Fabric Calculator does this instantly: enter pole width, drop, fullness, and fabric width, set the hem allowance, and read the live results—number of widths, cut length, and total fabric to buy with a 10% margin included.

Measuring for curtains can feel like guesswork. You measure the pole, decide on length, pick a fabric width, and hope you buy enough—but not too much. Most people either run short or end up with metres of leftover fabric. The problem is the maths: fullness ratios, hem allowances, and fabric widths all interact. A 2.5 m pole with 150 cm drop and 140 cm fabric needs more than just width × drop; you must account for fullness (usually 1.5 to 2.5) and turnings (20–25 cm). Doing this by hand risks mistakes, especially when the fabric width doesn’t divide evenly into the fullness-adjusted pole width. That’s where the Curtain Fabric Calculator comes in: it handles the maths instantly, so you buy the exact amount.

What You Need Before You Start

You only need four measurements to calculate curtain fabric:

Track or pole width (the horizontal space the curtains will cover)
Finished curtain drop (from pole to where you want the curtains to end)
Fullness ratio (how gathered you want the curtains—1.5 for light gather, 2.0 for standard, 2.5 for heavy gather)
Fabric width (the usable width of your chosen fabric, usually 110–150 cm)

You also need to decide on the hem and heading allowance. A typical allowance is 20–25 cm (8–10 inches), which covers the top heading (where the curtain hooks attach) and the bottom hem. If your fabric has a pattern repeat, you may need extra length to match the pattern across widths—this is not included in the calculator, so add it manually if needed.

How to Calculate Curtain Fabric with the Online Tool

Open the Curtain Fabric Calculator in your browser.
Select your units (metric or imperial).
Enter the track or pole width (e.g., 250 cm).
Enter the finished curtain drop (e.g., 180 cm).
Set the fullness ratio (e.g., 2.0 for standard gather).
Enter the fabric width (e.g., 140 cm).
Set the hem and heading allowance (e.g., 25 cm).
Read the results live:
- Number of fabric widths to cut (e.g., 4 widths).
- Cut length per width (e.g., 205 cm).
- Total fabric to buy (e.g., 8.2 m, which includes a 10% margin).

Why the Calculator Works Better Than Manual Maths

Manual calculations for curtain fabric involve multiple steps: multiply the pole width by the fullness ratio, divide by the fabric width to find the number of widths, then add hem and heading allowances to the drop. Each step risks rounding errors or miscalculations. For example, a 2.5 m pole with 2.0 fullness and 140 cm fabric width gives 3.57 widths—you can’t buy half a width, so you round up to 4 widths. The calculator does this automatically and adds a 10% margin to cover cutting errors or fabric shrinkage after washing. It also updates results live as you adjust measurements, so you can experiment with different fullness ratios or fabric widths without recalculating.

The calculator is especially useful for patterned fabrics. While it doesn’t account for pattern repeats, the live results let you see how much extra length you need to add per width to match the pattern. For example, if your fabric has a 64 cm pattern repeat and the calculator shows a cut length of 205 cm, you might round up to 256 cm (4 × 64 cm) to ensure the pattern matches across all widths. This flexibility is hard to achieve with manual calculations.

Common Mistakes and How to Avoid Them

Mistake	Why It Happens	How to Avoid It
Buying too little fabric	Forgetting to account for fullness or hem allowances	Use the calculator’s 10% margin and set the hem allowance to 20–25 cm
Buying too much fabric	Rounding up too aggressively or ignoring fabric width	Enter the exact fabric width into the calculator to minimise waste
Mismatched patterns	Not accounting for pattern repeats in the cut length	Add the pattern repeat length to the calculator’s cut length result
Uneven gathers	Using the wrong fullness ratio for the fabric weight	Use 1.5 for lightweight fabrics, 2.0 for medium, and 2.5 for heavy fabrics

Another common mistake is measuring the pole width incorrectly. Always measure the full width of the pole or track, not just the window. If the pole extends beyond the window (as it should for proper light control), include that extra width in your measurement. The calculator’s live results help here: if the number of widths seems too high or low, double-check your pole width measurement.

How to Adjust for Different Curtain Styles

Curtain styles affect the fullness ratio and hem allowance. Here’s how to adjust the calculator for common styles:

Pencil pleat: Use a fullness ratio of 2.0–2.5 and a hem allowance of 20–25 cm. Pencil pleats need more gather for a full look.
Eyelet (grommet): Use a fullness ratio of 1.5–2.0 and a hem allowance of 15–20 cm. Eyelet curtains hang flatter, so less gather is needed.
Tab top: Use a fullness ratio of 1.5 and a hem allowance of 15 cm. Tab tops have minimal gather and a shorter heading.
Wave (S-fold): Use a fullness ratio of 2.0–2.5 and a hem allowance of 20–25 cm. Wave headings need extra fabric for the folds.

If you’re unsure about the fullness ratio, start with 2.0 and adjust in the calculator. The live results will show how the number of widths and total fabric change as you tweak the ratio.

What to Do with the Results

Once you have the results from the calculator, use them to buy fabric confidently. The calculator gives three key numbers:

Number of widths: This tells you how many strips of fabric to cut. For example, if the calculator shows 4 widths, you’ll cut 4 strips from the fabric bolt.
Cut length per width: This is the length of each strip, including hem and heading allowances. For example, if the result is 205 cm, each strip should be 205 cm long.
Total fabric to buy: This is the total metres or yards to purchase, including the 10% margin. For example, if the result is 8.2 m, buy 8.2 m of fabric.

If your fabric has a directional pattern or nap (like velvet), buy extra to account for matching the pattern or aligning the nap. The calculator’s 10% margin usually covers this, but check the fabric’s pattern repeat and adjust if needed.

For large projects, like floor-to-ceiling curtains in a living room, consider using the Flooring Calculator to estimate how much fabric you’ll need for multiple windows. The process is similar: measure each window, calculate the fabric for each, and sum the totals. The Curtain Fabric Calculator’s live results make this easy—just note the total fabric for each window and add them together.

How the Calculator Handles Edge Cases

The calculator is designed to handle edge cases that manual calculations struggle with. For example:

Very wide poles: If the pole width is much larger than the fabric width (e.g., 4 m pole with 140 cm fabric), the calculator will show a high number of widths (e.g., 6 widths for 4 m pole with 2.0 fullness). This is correct—wide poles need more fabric to achieve the desired gather.
Narrow fabric: If the fabric width is very narrow (e.g., 110 cm), the calculator will show more widths than with wider fabric. This is expected, as narrow fabric requires more strips to cover the same pole width.
Short drops: For café curtains or short drops, the calculator still adds the hem allowance. If the allowance seems too large for the drop (e.g., 25 cm allowance on a 50 cm drop), reduce the allowance to 10–15 cm.

The calculator also handles imperial units (inches and yards) seamlessly. If you measure in inches, select imperial units and enter the measurements as you took them. The results will show in yards, which is how fabric is typically sold in the US and UK.

How to Double-Check Your Measurements

Before buying fabric, double-check your measurements to avoid costly mistakes. Here’s how:

Pole width: Measure the pole or track from end to end, not just the window. If the pole extends beyond the window, include that extra width.
Finished drop: Decide where the curtains will end—just below the window sill, to the floor, or puddled on the floor. Measure from the pole to that point.
Fabric width: Check the fabric’s label or ask the shop for the usable width. Some fabrics have selvedges (finished edges) that reduce the usable width.
Fullness ratio: Use 1.5 for lightweight fabrics, 2.0 for medium, and 2.5 for heavy fabrics. If unsure, start with 2.0 and adjust in the calculator.

If you’re measuring for multiple windows, measure each one separately. Even windows that look the same can have slight differences in width or drop. The calculator’s live results make it easy to compare measurements and spot inconsistencies.

How to Use the Calculator for Lined Curtains

Lined curtains need extra fabric for the lining. The Curtain Fabric Calculator only calculates the main fabric, so you’ll need to calculate the lining separately. Here’s how:

Use the calculator to find the main fabric requirements (number of widths, cut length, total fabric).
For the lining, use the same number of widths and cut length as the main fabric, but with the lining fabric’s width (usually 137–150 cm).
Calculate the total lining fabric: number of widths × cut length, then add 10% for margin.

For example, if the calculator shows 4 widths and 205 cm cut length for the main fabric, and the lining fabric is 150 cm wide, you’ll need 4 widths × 205 cm = 8.2 m of lining fabric (including 10% margin).

If you’re using interlining (an extra layer for insulation or body), calculate it the same way as the lining. The calculator’s results for the main fabric give you the base numbers to work from.

How to Save Money on Curtain Fabric

Curtain fabric can be expensive, especially for large windows or premium fabrics. Here’s how to save money without compromising on quality:

Choose wider fabric: Wider fabric (e.g., 150 cm instead of 110 cm) reduces the number of widths needed, which can lower the total fabric required. The calculator’s live results let you compare different fabric widths instantly.
Adjust the fullness ratio: A fullness ratio of 1.5 uses less fabric than 2.5. If you’re on a budget, opt for less gather. The calculator shows how much fabric you’ll save by reducing the ratio.
Buy remnants: Fabric shops often sell remnants (leftover pieces) at a discount. Use the calculator to see if a remnant’s length matches your cut length. For example, if the calculator shows a cut length of 205 cm and you find a 2.2 m remnant, it might work.
Reuse old curtains: If you’re replacing old curtains, check if the fabric can be repurposed. Measure the old curtains and compare to the calculator’s results—you might only need to buy a little extra fabric to make up the difference.

The calculator’s 10% margin is designed to minimise waste, but it’s still worth checking for sales or remnants. The live results make it easy to experiment with different measurements and see how they affect the total fabric needed.