Convert Sewing Pattern Measurements to Centimeters

Direct answer

Multiply each sewing measurement in inches by 2.54 to convert it to centimeters.

For example, a 5/8-inch seam allowance converts as follows:

In practical sewing, this may be marked as approximately 1.6 centimeters when the pattern and technique allow that rounding.

How to convert sewing measurements

1. Identify the original inch measurement. Determine whether it describes a seam allowance, garment dimension, body measurement, hem, or fabric cut.
2. Convert any fraction to a decimal. For example, 3/8 inch becomes 0.375 inch.
3. Multiply by 2.54. Apply the exact conversion factor to the full value.
4. Choose a suitable rounding level. Avoid rounding so much that the finished garment or project is altered noticeably.
5. Use one measurement system consistently. Avoid switching repeatedly between inches and centimeters during the same cutting or sewing process.

Common seam allowances in centimeters

A rounded practical value should only be used when it matches the pattern instructions and the required construction accuracy.

Example: convert a 3/8-inch seam allowance

This is commonly treated as approximately 1 centimeter. The difference is small, but the same rounded interpretation should be used consistently along the entire seam.

Example: convert a 5/8-inch seam allowance

This may be marked as 1.6 centimeters when measuring with a metric ruler. Avoid reducing it to 1.5 centimeters unless the pattern allows that change.

Converting body measurements

Body measurements may include bust, chest, waist, hip, sleeve, shoulder, inseam, rise, and garment length. Convert each value separately and preserve the label.

Example: convert a 36-inch bust measurement

Example: convert a 28.5-inch waist measurement

Pattern size charts may already use rounded centimeter values. Compare the original chart rather than assuming every metric value is an exact conversion.

Converting fabric dimensions

Fabric width, cut length, strips, squares, and pattern pieces can all require conversion.

Example: convert 45-inch-wide fabric

Example: convert a 6.5-inch fabric square

For squares and rectangles, convert both dimensions separately. A 6.5 x 6.5-inch square is 16.51 x 16.51 centimeters.

Converting hem allowances

Hem instructions may require folding fabric by a specified amount, such as 1/2 inch followed by another 1 inch.

Mark each fold separately. Do not add the two values unless the instructions describe the total hem depth.

Should sewing conversions be rounded?

Some sewing measurements can be rounded slightly without affecting the finished result, while others require closer precision.

• Seam allowances should remain consistent along the seam.
• Quilting pieces may require greater precision because small differences accumulate across many pieces.
• Loose garment measurements may tolerate modest rounding.
• Fitted garments and pattern alterations may require more precise values.
• Decorative spacing should be measured consistently even when the exact converted number is inconvenient.

Avoid mixing inches and centimeters

Converting only part of a pattern can lead to inconsistent seam allowances and mismatched pieces. Once a project has been converted, use the same system for all related measurements.

Keep notes showing:

• the original inch value;
• the converted centimeter value;
• any rounded working value;
• the part of the pattern where it applies.

The Inches to Centimeters Converter accepts whole, decimal, and fractional-inch measurements.

Common sewing conversion mistakes

Rounding every fraction to a whole centimeter

This can change seam allowances significantly. For example, 5/8 inch is closer to 1.6 centimeters than to 1 centimeter.

Changing only some measurements

Pattern pieces and construction instructions should use a consistent system.

Confusing finished size with seam allowance

A pattern piece may include seam allowance beyond the finished garment dimensions.

Ignoring repeated small differences

A small rounding difference can become significant when repeated across multiple seams, pleats, blocks, or panels.

Related inches to centimeters guides

Frequently asked questions