1 Most commercial patterns are not equivalent to the sizes we get off the peg, so the first step to grading is to take accurate body measurements. Start with your hips, bust and waist, then compare these measurements to those on the back of the envelope.

2 The actual finished measurements of the garment, including the amount of ease, is usually written on the pattern pieces, so use this to check the final fit. If you still find that you need to alter it, then it’s time to grade the pattern pieces.

3 Once you’ve accurately measured your body, select the pattern pieces you need for the garment and roughly cut them out, leaving as much extra paper outside of the largest size as possible. Take a 15cm ruler and place it across the junction of all parts of the pattern, including shoulder seams, darts and sleeves. Draw guidelines through these points.

4 Start with the side seam and work out the distance in between each of the sizes. If the difference between them is the same, add this length along each grading line and join these points to create the next size up or down. If the difference in between each size shows a progressive change, then calculate the measurement required and draw it in.

5 On curved areas, such as armholes and necklines, measure and mark around four or five points along the curve to the size you need, then draw in the new size using a French curve ruler. Make sure you record any notches too and move them across to the next size. This tool is invaluable for pattern grading as it will allow you to maintain the original shape of the garment, while proportionally increasing or decreasing the size of a pattern.

6 To draw the new size, join up the grading lines around the edge of all of the pattern pieces and make sure you include any facings and darts, then you can sew the garment as normal. Voila – it’s as simple as that!