Precise measuring up and cutting out are the crucial first steps to sewing curtains that hang well.

Your choice of custom made blinds will depend largely on the size and shape of your window, other soft furnishings in the room and the visual effect you want to create. This guide to measuring cup can be used for all straight-fall, fabric curtains, lined or unlined, made with tape headings. (Available by the meter from haberdashery departments, heading taped are attached to the top of the drapes as the quickest and easiest way of pleating and hanging them).

You need the following information to calculate the total fabric required to make curtains for a window.

The width of the curtain track or pole.    The finished gathered width of each curtain.    The fabric requirement of the curtain heading tape.    The desired curtain length.    The pattern repeat.

A tip to think about: If possible, use a retractable steel tape – the type sold for DIY – rather than a dressmaker’s tape to measure the window’s dimensions. A steel tape is longer and will give a more accurate measurement.

A curtain track or pole:

Before measuring up for curtains fix the track or pole you plan to use in place so that its exact height and width can be measure. As a guide, fix the track or pole between 3-5 inches (7.5 – 12.5cm) above the window and allow at least 6 inches (15cm) overlap on each side, unless it is in a recess so that the curtain can be swept back away from the window to let in maximum light.

Curtain width:

First, simply measure the length of the track or pole and divide this measurement by two for a pair of curtains. For certain tracks, you will have to add extra fabric for an overlap between the two curtains in the center, so check the instructions with the track.

Heading tape:

Now, choose the heading tape you want to use – you will need to know this before you can work out the final fabric amounts because the gathering allowance for different styles of heading tape varies, as the chart shows. As a general guide, you will need at least 1 1/2-2 times the width of the curtain to achieve the necessary fullness.

Heading tape Fabric needed

Standard tape 1 1/2-2 x

Pencil pleat tape 2 1/2-3 x

Triple pleat 2 x Gathered

Cartridge pleat 2 x curtain

Box pleat 3 x width

Goblet pleat 2 x

Smocked tape 2 x

Curtain Length:

There are three popular curtain lengths:

Sill length – the curtain hems are 3/8 inch (1cm) above the sill so that they sweep clear of it.    Below the sill – the curtains hang best if they are between 4-6 inches (10-15cm) below the sill.    Floor-length – the curtain hems are 3/8 inch (1cm) above the floor to prevent wear.

For the curtain length, measure from the top of the fixed curtain track, or from the base of the rings on the curtain pole to the desired position of the lower edge of the curtain. Ignore heading seam and hem allowances at this stage; they are added on later when calculating fabric quantity.

Pattern repeat:

For patterned fabrics, you will need to buy extra so that you can match up the pattern across the width and when the curtains are drawn together. Make allowances, too, for any overlap between the closed curtains. To work out the extra fabric required, you have to know the pattern repeat.

To find the pattern repeat allowance, measure the distance along the selvage edge between one pattern motif and the same point on the next identical one. Look out for this when you are choosing the fabric; it is often quoted on a details’ label. In general, add one extra pattern repeat for every fabric width required.

When calculating fabric quantity makes sure you always use accurate measurements and measure up all windows separately even if they look identical.

Only work with full and half fabric widths. If your calculations fall the odd bit over a convenient width, ease off the gathering on the heading tape slightly, rather than add another half-width of the fabric.

When cutting out find a large flat surface – a clean floor is ideal – that will take the complete curtain length and width. For matching patterned fabrics, you also need to be able to lay two widths side by side.

1. Preparing to cut: Lay the fabric flat, right side up. On patterned fabrics, plan, and then mark the position of the base; for the best effect, the complete pattern, or a clear section of it, should sit along the base of the curtain after the hem has been turned up.
2. Straightening up the base edge: Use a large set square to mark the base edge at right angles out from the selvage. Then cut the fabric along the marked line.
3. Cutting out: Measure the curtain length up from the base edge and, again using a large set square and ruler, mark the top edge and cut along it. To cut the second length, place the uncut fabric against the cut length and match any pattern design across the two pieces. Cut the remaining lengths in the same way.

You may need to join the lengths of fabric together to make the total ungathered width for each curtain. If the curtain contains full widths and a half, place the half widths on the outer edge.

1. Joining widths: Pin the fabric widths together, right sides facing, and then look on the right side to check that the pattern matches. To be sure of an exact match, hold the lengths together using a ladder stitch.
2. Stitching widths: Machine stitch the widths together taking a 5/8 inch (1.5cm) seam allowance. Press the seams to one side, trim to 1/4 inch (6mm), then neaten them with a zigzag stitch or over-lock them and remove any ladder stitching. Alternatively, for unlined curtains, you can use a French seam.

The pattern repeat on some fabrics can be quite large, so after cutting out your curtain widths use spare pieces of fabric to make matching tiebacks or scatter cushions.