Ready Made Curtain Size Calculator: Find Your Fit

This calculator works out the ready-made curtain width and drop you need for your window, based on the track or pole length, your desired fullness, and the finished length you want. You enter your window measurements and preferences, and it returns the closest standard curtain sizes in both inches and centimeters, so you can shop with confidence. The result is a set of recommended widths and drops that match common ready-made sizes.

Formula

The calculator uses two simple formulas that mirror how curtain manufacturers and retailers size their products:

• Curtain width per panel = (Track/Pole Width × Fullness Ratio) ÷ Number of Panels (assumed 2 for a standard pair).
• Curtain drop = Finished Drop + Header Allowance.

Variables:

• Track/Pole Width (tw) – the full width of your curtain track or pole, in inches (or cm if you prefer, but keep units consistent).
• Fullness Ratio (fl) – how much fabric you want relative to the track width. 1.5 is minimal, 2 is standard, 2.5–3 is luxurious. This is a unitless number.
• Finished Drop (fl2) – the length from the top of the track or pole to where you want the curtain to end (floor, sill, or apron), in inches.
• Header Allowance (hd) – extra fabric above the finished drop for the heading style (e.g., pencil pleat tape, eyelet rings, or a rod pocket). This is typically 2–4 inches, in inches.

The width formula assumes you are buying a pair of curtains (two panels). If you use a single panel, divide by 1 instead of 2. The drop formula adds the header allowance because the finished drop is measured from the top of the track, but the curtain fabric extends above that point to form the heading.

Worked Example

Using the default values from the calculator:

• Track/Pole Width = 48 inches
• Fullness Ratio = 2
• Finished Drop = 84 inches
• Header Allowance = 3 inches

Step 1: Calculate width per panel.

Width per panel = (48 × 2) ÷ 2 = 48 inches. This means each panel should be 48 inches wide (before hemming allowances, which are already included in ready-made sizes).

Step 2: Calculate drop.

Drop = 84 + 3 = 87 inches. This is the total fabric length of the curtain.

Step 3: Convert to centimeters (if needed).

Width per panel = 48 × 2.54 = 121.9 cm, roughly 122 cm.

Drop = 87 × 2.54 = 221 cm, roughly 221 cm.

So for a 48-inch track with standard fullness, you would look for ready-made curtains that are approximately 48 inches (122 cm) wide per panel and 87 inches (221 cm) long. In practice, you would choose the nearest standard size, often 50 inches wide and 90 inches long.

Understanding Ready-Made Curtain Sizes

Ready-made curtains are sold in standardized widths and drops, usually in even numbers. Common widths per panel are 46, 50, 54, 66, 72, and 90 inches (or 117, 127, 137, 168, 183, and 229 cm). Common drops are 54, 63, 72, 84, 90, 96, and 108 inches (or 137, 160, 183, 213, 229, 244, and 274 cm). These sizes are designed to fit a range of standard windows, but they rarely match your exact measurements. The calculator gives you a target size, and you choose the closest ready-made option that meets or slightly exceeds that size.

Why does fullness matter? A curtain that is exactly the width of the window looks flat and stretched. Fullness adds gathers and pleats, giving a richer appearance. A ratio of 1.5 is common for sheer or lightweight fabrics, 2 is the standard for most curtains, and 2.5–3 is used for formal or heavy fabrics. If you are using eyelet curtains, a ratio of 1.5–2 is typical because the eyelets create a natural gather. For pencil pleat, a ratio of 2–2.5 is recommended.

How to Choose the Right Size

1. Measure the track or pole width – not the window frame. For a pole, measure from end to end, excluding the finials. For a track, measure the full track length.
2. Decide on the fullness ratio – based on fabric type and desired look. When in doubt, use 2.
3. Decide on the finished drop – measure from the top of the track or pole (not the rod itself if it has rings) to the floor, sill, or just below the apron. For floor-length curtains, add 1 inch if you want them to hover just above the floor, or 6–8 inches for a puddle effect.
4. Add the header allowance – this is often already included in the ready-made drop, but if you are buying custom or making your own, add 2–4 inches for the heading.
5. Calculate and round up – the calculator gives you a precise number, but ready-made sizes are fixed. Always round up to the nearest standard size. For example, if you need 48 inches, a 50-inch panel is fine; if you need 68 inches, choose 72 inches.

Common Mistakes and Misconceptions

One of the most common mistakes is measuring the window glass instead of the track or pole. The track is usually 4–8 inches wider than the window to allow the curtains to clear the glass when open. Another mistake is ignoring the header allowance – if you measure from the top of the track and then buy a curtain with a 3-inch header, the curtain will be 3 inches too long. Always check the product description: some ready-made curtains list the drop as the total length including the header, while others list the finished drop excluding the header. The calculator assumes you are adding the header allowance to the finished drop, so if the product lists the total length, you can skip the header allowance.

A common misconception is that curtains should be exactly the width of the window. In reality, a flat curtain looks sparse. Fullness is what gives a professional look. Another misconception is that you can use the same width for all window types – bay windows or corner windows may require separate curtains for each section, and the calculator works per panel, so you may need to adjust.

Comparing Ready-Made vs. Custom Curtains

Ready-made curtains are cheaper and faster to buy, but they come in limited sizes. Custom curtains are made to your exact measurements, so they fit perfectly, but they cost more and take weeks to produce. The calculator helps you decide if a ready-made size is close enough. If your required size is within 2–3 inches of a standard size, ready-made is usually fine. If the difference is more than that, you might need to look for a different size or consider custom. Also, ready-made curtains often have a standard header style (e.g., eyelet, pencil pleat, or tab top), which may not match your track or pole. For example, eyelet curtains require a pole (not a track) and have a specific drop measurement from the top of the pole to the floor, not including the rings.

Cost and Practical Considerations

Ready-made curtains are typically sold per panel, and the price increases with width and drop. Buying two panels that are wider than needed means more fabric and a higher cost, but it also gives a fuller look. You can sometimes buy a single panel if you have a narrow window, but most retailers sell in pairs. The calculator’s output helps you avoid overbuying: if you need 48 inches per panel, you don’t need to buy 60-inch panels unless you want extra fullness. However, if you are between sizes, it is better to go up rather than down, because a slightly wider curtain can be gathered more, while a narrower one will look stretched.

Limitations of the Calculator

This calculator assumes a standard pair of curtains on a straight track or pole. It does not account for:

• Bay windows – each section needs its own width calculation.
• Curtains that wrap around corners – you need to measure each straight run separately.
• Special heading styles – some headings, like goblet pleats, require more fullness (up to 3.5), while others like eyelets work with less.
• Fabric pattern repeats – if the fabric has a large pattern, you may need extra fabric to match the pattern across panels, which can affect the drop.
• Hemming allowances – ready-made curtains usually have a 2–4 inch hem, but if you are shortening them, you need to account for the new hem.

Always double-check your measurements and, if in doubt, consult the retailer’s sizing guide or a professional curtain fitter.

Frequently Asked Questions

What fullness ratio should I use? For most curtains, a ratio of 2 is standard. If you want a more casual, relaxed look, use 1.5. For a formal, luxurious look, use 2.5–3. Sheer fabrics often look better with 2–2.5 because they are lighter and need more gather to look substantial.

How do I measure the drop for eyelet curtains? For eyelet curtains, measure from the top of the pole (not the rings) to the floor, then add 1–2 inches so the bottom just clears the floor. The eyelet header is usually about 1.5 inches, so the fabric length is the drop plus that header. This calculator’s header allowance covers that.

Can I use this calculator for a single curtain panel? Yes, but you need to change the divisor in the width formula from 2 to 1. The calculator assumes a pair, so for a single panel, multiply the track width by the fullness ratio and use that as the width per panel.

What if my window is wider than 600 inches? The calculator’s maximum track width is 600 inches, which covers most residential windows. For commercial or very large windows, you would likely need multiple panels or custom curtains. In that case, divide the track into sections and calculate each separately.

Should I round up or down to the nearest ready-made size? Always round up. If the calculator says you need 47 inches, choose a 50-inch panel. If you choose a 46-inch panel, the curtain will be too narrow and will look stretched when closed. Rounding up gives you extra fabric to play with, and you can always take it in if needed.

Does the header allowance vary by curtain style? Yes, it does. Pencil pleat tape usually needs 2–3 inches, eyelets need about 1.5–2 inches, and rod pockets need the diameter of the rod plus a little extra. If you are unsure, check the product description or measure the header of an existing curtain.

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in tw | Track/Pole Width | in | 48 | 0 | 600
in fl | Fullness Ratio | - | 2 | 1 | 3
in fl2 | Finished Drop (from top of track) | in | 84 | 0 | 150
in hd | Header Allowance | in | 3 | 0 | 12
out cw | Curtain Width per Panel | in | (tw * fl) / 2 | 1
out cd | Curtain Drop | in | fl2 + hd | 1
out cwcm | Width per Panel (cm) | cm | ((tw * fl) / 2) * 2.54 | 1
out cdcm | Drop (cm) | cm | (fl2 + hd) * 2.54 | 1