How to Write Product Dimensions in CM and Inches
Product dimensions look simple until a buyer, marketplace feed, shipping system, or supplier reads them differently. A size like 30 x 20 x 10 cm is useful only when the reader knows the order of the sides, the unit, and whether the measurement describes the product itself or the shipping package.
This guide is not another cm-to-inches calculator. It is a practical way to write dimensions so people can understand the size quickly and systems can parse the data cleanly. When you need the actual math, use the length converter, cm to inches, or inches to cm tools.
Use One Clear Order: Length x Width x Height
For most product listings and packaging notes, write the three sides as length x width x height. Length is usually the longest side of the product or box base, width is the shorter side across the base, and height is the vertical measurement. This order is common in ecommerce, shipping, and manufacturing. It is also the order used in Google Merchant Center product feeds. If you use a different order, make sure to label the sides clearly to avoid confusion.
Good listing format
Product size: 30 x 20 x 10 cm (11.81 x 7.87 x 3.94 in)
This keeps the order, units, and converted values visible in one line.
Show the Primary Buyer Unit First
If most of your buyers think in centimeters, put centimeters first. If the listing is mainly for US buyers, put inches first and add centimeters in parentheses. The goal is not to prove the math. The goal is to help the shopper judge whether the item fits a shelf, desk, wall, bag, frame, or room.
| Audience | Recommended display | Why it works |
|---|---|---|
| International shoppers | 30 x 20 x 10 cm (11.81 x 7.87 x 3.94 in) | Metric first, inch reference included. |
| US shoppers | 11.8 x 7.9 x 3.9 in (30 x 20 x 10 cm) | Inches first, metric still available. |
| Technical specs | 300 x 200 x 100 mm | Millimeters keep small tolerances readable. |
Do Not Mix Product Size and Shipping Size
Product size describes the item. Shipping size describes the packed box or mailer. They are not the same measurement, and mixing them can create wrong customer expectations or wrong shipping calculations. If both matter, label both:
- Product size: 30 x 20 x 10 cm
- Package size: 34 x 24 x 14 cm
- Product weight and package weight should be separated in the same way.
Google Merchant Center also separates product dimensions from shipping
dimensions, and supports product length, width, and height values in
cm or in. Keeping the same unit across all three
product dimension fields helps the data display cleanly.
Round for Humans, Store for Accuracy
A converted value like 11.8110236 inches is technically precise, but it is not pleasant in a listing. For customer-facing product pages, one or two decimals is usually enough. For manufacturing, CAD, or inspection notes, keep the exact working value and round only in the final display.
If the dimension is small or technical, convert through millimeters instead. The cm to mm and inches to mm converters are better choices for parts, holes, clearances, hardware, and 3D printing notes.
A Simple Publishing Checklist
- Use one order consistently: length x width x height.
- Write the unit after the full set of dimensions.
- Show the buyer's familiar unit first.
- Separate product dimensions from package dimensions.
- Keep all three dimensions in the same unit inside product feeds.
- Use millimeters when tolerance or small-part fit matters.
When You Need a Converter
For a single product size, convert the full dimension set once and publish both units. For repeated catalog work, keep one source unit in your product database and generate the alternate display automatically. Start from the length conversion hub when you need several unit pairs, or jump directly to centimeters to inches, inches to centimeters, millimeters to inches, and inches to millimeters.
References
For product feed requirements, see Google Merchant Center product dimension attributes.