What is a seam allowance?

A seam allowance is the extra fabric between the cut edge and the stitching line. It holds the seam together and allows for adjustments. Common values are 5/8 inch (1.6 cm) in US patterns and 1.5 cm (roughly 5/8 inch) in European patterns.

What is the standard seam allowance in inches?

The most common seam allowance in US dressmaking patterns is 5/8 inch (0.625 in = 15.875 mm). Quilting patterns typically use 1/4 inch (0.25 in = 6.35 mm).

What is the standard seam allowance in centimeters?

European and international patterns commonly use 1.5 cm (15 mm = approx. 0.591 in). Some patterns use 1 cm or 2 cm depending on the garment type.

How many millimeters is 5/8 inch?

Five-eighths of an inch equals exactly 15.875 mm, or approximately 1.588 cm. This is the most frequently used seam allowance in American sewing patterns.

Can I use this tool for quilting seam allowances?

Yes. Quilting typically requires a precise 1/4 inch (6.35 mm / 0.635 cm) seam allowance. Simply type 0.25 in the inches field or select the 1/4 in quick-select button.

Seam Allowance Converter

Name: Seam Allowance Converter
Availability: InStock
Author: Nham Vu

Enter a seam allowance value in inches, centimeters, or millimeters and instantly get the equivalent in all other units.

Enter Measurement

Type a value and choose a unit — all other units update instantly.

Inches (in)

Centimeters (cm)

Millimeters (mm)

Common Seam Allowances

Converted Values

Results update as you type in any field above.

Inches

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Centimeters

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Millimeters

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Summary

Enter a seam allowance value in inches, centimeters, or millimeters and instantly get the equivalent in all other units.

How it works

Select the unit you want to convert from (inches, centimeters, or millimeters).
Enter your seam allowance measurement in the input field.
The tool instantly shows the equivalent values in the other two units.
Use the quick-select buttons to jump to common seam allowances.
Click "Copy Results" to copy all converted values to your clipboard.

Use cases

Converting a pattern seam allowance from inches to metric for international use.
Translating European sewing patterns (cm/mm) to imperial measurements.
Checking that a 5/8 inch standard seam allowance equals roughly 1.6 cm.
Verifying seam widths when switching between imperial and metric rulers.
Teaching students the relationship between sewing units of measurement.
Quickly converting overlocking/serger margin settings between unit systems.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu