Seam Allowance Calculator

Seam Allowance Calculator

Adds or removes seam allowance from pattern measurements. Enter the cut size and desired seam allowance to get the finished size, or enter the finished size to calculate the cut size needed.

Standard seam allowances

Why seam allowance matters

Seam allowance is the fabric between the cut edge and the stitching line. It must be consistent throughout a garment, mismatched seam allowances cause pattern pieces to not align correctly at seams. When adapting patterns from different countries or eras, convert the seam allowance convention to avoid fit issues.

Tips

• Mark the stitching line with tailor's chalk, not just the cut edge
• Clip curved seams within the allowance to allow the seam to lie flat
• Press seams open or to one side depending on the fabric and desired finish

UK and international pattern conventions

Seam allowance conventions vary significantly between pattern publishers and countries , a common source of fit errors when mixing patterns:

• UK home sewing (Simplicity UK, Vogue, McCall's): seam allowance is included in the printed pattern pieces. Standard is 1.5 cm (5/8 inch). The cutting line is the outer edge; the stitching line is inside.
• Burda (Germany): seam allowance is NOT included. Burda magazine patterns print the stitching line only , you must add your own seam allowance when cutting. The default Burda allowance to add is 1.5 cm for most seams and 2-3 cm for hems. This is the most common trap when sewing from a Burda pattern for the first time.
• Vintage UK patterns (1950s-1970s): often printed in inches with 5/8 inch (1.5 cm) seam allowance included, but check each pattern , earlier patterns sometimes used 1/2 inch.
• Japanese patterns: seam allowance often NOT included; stated explicitly in the pattern instructions.