Work out the fabric width for your curtains
Getting curtain widths right is the difference between curtains that hang beautifully with full, even gathers and curtains that look flat and skimpy. The total fabric width you need depends on the window width, the heading type (which determines how much the fabric is gathered), and whether you allow for stack-back space so the curtains clear the window when open. In the UK, curtains are typically made as pairs (two panels), one for each side of the window. The heading type determines the fullness multiplier: pencil pleat curtains need twice the track width in fabric, eyelet and tab-top curtains need one and a half times, and traditional pinch pleat curtains need two and a half times for their deep, structured folds. These multipliers are industry standards used by curtain makers across Britain. Stack-back refers to the space where curtains sit when fully drawn open. Adding 15cm on each side of the window ensures the curtains do not block any of the glass when open, maximising natural daylight. This is particularly important for smaller windows or north-facing rooms in the UK where natural light is precious. The calculator determines the pole or track width including stack-back, then applies the appropriate fullness multiplier to give you the total fabric width needed, as well as the width per panel.
To calculate the fabric width for your curtains: 1. Measure the window width in metres. Measure the actual window opening, not the wall. If you already have a curtain pole, measure the pole length instead and turn off the stack-back option. 2. Select the heading type. Pencil pleat is the most common in UK homes and works with tracks or poles. Eyelet is modern and casual, best on poles. Tab-top is informal. Pinch pleat is the most luxurious option. 3. Toggle stack-back on if you want curtains to clear the window completely when open. This adds 15cm to each side. Turn it off if space is limited or if you are measuring from an existing pole. 4. Enter the number of panels. Two is standard (one per side). Use one panel for a door curtain or asymmetric design. 5. Review the total fabric width and per-panel width. When shopping for fabric, the per-panel width tells you how many widths of fabric (typically 137cm wide in the UK) you need to join together for each curtain panel.
The curtain width calculation involves three steps: First, determine the pole or track width. Start with the window width and add the stack-back allowance. For a 1.8m window with stack-back: 1.8 + 0.30 = 2.1m (15cm each side). Second, apply the fullness multiplier based on the heading type. For pencil pleat (2.0x): 2.1 x 2.0 = 4.2m total fabric width. Third, divide by the number of panels. For two panels: 4.2 / 2 = 2.1m per panel. Standard UK curtain fabric is 137cm (54 inches) wide. If each panel needs to be 2.1m wide, you need two widths of fabric joined together per panel (since 137cm is only 1.37m). This means you need 4 fabric widths in total, each cut to your drop length. Fullness multiplier reference: pencil pleat 2.0x, eyelet 1.5x, tab-top 1.5x, pinch pleat 2.5x. These are the standard ratios recommended by UK curtain manufacturers and soft furnishing courses. For eyelet curtains without stack-back on a 1.8m window: 1.8 x 1.5 = 2.7m total, or 1.35m per panel. This would require just one width of 137cm fabric per panel.
This calculator covers width only. For the drop (length), measure from the top of the pole or track to where you want the curtains to end. Standard options are sill length (ending 1cm above the sill), below sill (15cm below), or floor length (1cm above the floor). For puddle-effect curtains, add 5-15cm extra. Always order fabric from the same dye lot (batch number) to ensure colour consistency across panels. If using patterned fabric, you also need to account for pattern repeat when calculating the total fabric length.