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Seam Allowance Chart – Online Metric & Imperial Quick Ref

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Seam Allowance Chart

Quick reference for seam allowance conversions between inches and metric (mm/cm). Standard, narrow, and wide seam allowances for sewing, quilting, and pattern drafting.

Free Quick Reference Imperial & Metric
Seam Allowance Conversion Table
Inch (Fraction) Inch (Decimal) Millimeters Centimeters Common Use
1/8" 0.125" 3.2 mm 0.32 cm Topstitching edge
1/4" 0.25" 6.4 mm 0.64 cm Quilting, narrow seams
3/8" 0.375" 9.5 mm 0.95 cm Light fabrics, curves
1/2" 0.5" 12.7 mm 1.27 cm General sewing
5/8" ⭐ 0.625" 15.9 mm 1.59 cm US standard seam allowance
3/4" 0.75" 19.1 mm 1.91 cm Wide seams, alterations
7/8" 0.875" 22.2 mm 2.22 cm Loose-fit garments
1" 1.0" 25.4 mm 2.54 cm Hem allowances, wide seams
1 1/4" 1.25" 31.8 mm 3.18 cm Decorative hems
1 1/2" 1.5" 38.1 mm 3.81 cm Deep hems, tailoring
2" 2.0" 50.8 mm 5.08 cm Jacket hems, alterations

⭐ 5/8" (15.9 mm) is the most common standard seam allowance in US commercial patterns. Many European patterns use 1.5 cm as standard.

Live Converter

Enter any value — the other fields update instantly.

Supports fractions like 1/4, 3/8, 1 1/2
Closest standard: 5/8" (15.9 mm)
Visual Width Comparison (Proportional) — See how seam allowances compare at a glance
1/8"
3.2mm
1/4"
6.4mm
3/8"
9.5mm
1/2"
12.7mm
5/8" ⭐
15.9mm
3/4"
19.1mm
7/8"
22.2mm
1"
25.4mm
1 1/4"
31.8mm
1 1/2"
38.1mm

Bar widths are proportional. Narrow Standard Wide Extra Wide

Quilting

Typically 1/4" (6mm) — narrow and precise for piecing quilt blocks.

Garment Sewing

US standard: 5/8" (15mm). EU standard: 1.5cm.

Curves & Delicate

Narrow 3/8" (10mm) for curved seams and lightweight fabrics.

Tailoring & Hems

Wider 1"–2" (2.5–5cm) for jacket hems and alteration margins.

Frequently Asked Questions

A seam allowance is the distance between the fabric edge and the line of stitching. It ensures the seam has enough fabric to hold together without fraying and allows for adjustments. Standard seam allowances vary by country and project type — typically 5/8" (15.9 mm) in the US and 1.5 cm in many European patterns.

The industry standard for US commercial sewing patterns is 5/8 inch (approximately 15.9 mm or 1.59 cm). This has been the convention since the mid-20th century, providing enough room for fitting adjustments while not wasting fabric. Some pattern companies like Burda use 1.5 cm (about 0.59 inches) as their default.

Use the formula: 1 inch = 25.4 mm. Multiply the inch value by 25.4 to get millimeters. For example: 5/8" = 0.625 × 25.4 = 15.875 mm (rounded to 15.9 mm). Our live converter above does this calculation instantly — just type any value in the inch, mm, or cm field.

Quilting typically uses a 1/4 inch (6.4 mm) seam allowance. This narrow allowance reduces bulk in pieced quilt tops and is precise enough for matching points. Many sewing machines have a special 1/4" presser foot to help maintain this exact measurement consistently.

5/8 inch = 15.875 mm, which is typically rounded to 15.9 mm or 1.59 cm. In practice, many sewists round to 1.5 cm or 1.6 cm when marking seam allowances with metric rulers. The 0.1 cm difference is negligible for most garment sewing projects.

3/8 inch = 9.5 mm, while 1 cm = 10 mm. The difference is only 0.5 mm, which is negligible for most sewing projects. For curved seams or delicate fabrics, the tiny difference won't affect the final result. However, for precision tailoring or when multiple seams must align perfectly, it's best to be consistent with whichever measurement system you choose.

Use a seam gauge (a small ruler with a sliding marker) for the most accurate measurements. Many sewing machine needle plates have engraved guide lines at common seam allowances (3/8", 1/2", 5/8", etc.). You can also use washi tape or painter's tape on your machine bed to create a custom guide at your desired seam allowance.

Seam allowance standards are largely regional and historical. US companies (Simplicity, McCall's, Vogue) traditionally use 5/8". European companies like Burda use 1.5 cm. Japanese patterns often use 1 cm. Some indie pattern designers vary allowances based on the specific seam type. Always check the pattern instructions before cutting!

Seam allowance and seam margin are often used interchangeably, but technically there's a subtle difference. Seam allowance refers to the fabric between the cut edge and the stitch line. Seam margin sometimes refers specifically to the finished seam width after trimming or grading. In everyday sewing, both terms refer to the same thing — the extra fabric beyond the stitching line.
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