The short answer
Identify the exact item, name each axis, and state whether the measurements describe the product or its packaging. Convert units only after those facts agree. Compare against an explicit tolerance and preserve unresolved differences. Equal converted numbers do not establish physical fit.
Product dimensions and shipping dimensions answer different questions
A carton can be larger than its contents, and a nominal size can differ from a measured size. Before converting anything, label the item, the measurement basis, and the source location. Treat a package measurement and a product measurement as separate records even when their values happen to agree.
Google Merchant Center distinguishes product measurements from package measurements used for carrier-calculated shipping. Its product dimension guidance accepts centimetres or inches and calls for consistent units across dimensions. A local conversion tool supporting more units does not make those units valid in every destination.
| Record describes | Useful for | Do not infer |
|---|---|---|
| Assembled product | Describing the item being sold | Installation clearance or packaging size |
| Shipping package | Describing the packed shipment | The dimensions of the item inside |
| Nominal label or range | Identifying a size category or adjustment range | One exact physical measurement |
Source: Google Merchant Center: Product dimensions and weight; Google Merchant Center: Shipping dimensions
Compare two dimension records in your browser
Enter the same item’s length, width, and height from two sources. Choose product or shipping package for each record, name the source, and supply an allowed difference in millimetres. The fictional example is ready to compare; choose Start blank to enter your own records.
The result converts each named axis to millimetres and reports agreement, differences, or details that need review. Editing an input clears the old result. Download comparison saves your inputs and result locally; nothing entered in the checker is uploaded or stored by it.
Fictional example: the same stand described in inches and centimetres. Enter decimal values, such as 0.5 for half an inch. Your entries are not uploaded or saved.
Keep length, width, and height on their original axes. This checks supplied measurements only; it does not verify installation clearance, compatibility, or feed acceptance. The downloadable checker uses the same comparison rules.
Which dimension fields belong in a Google product feed?
Use product_length, product_width, and product_height for the item itself. Use shipping_length, shipping_width, and shipping_height for its package. A correct number in the wrong family of fields still describes the wrong object.
Google’s product dimension fields accept cm or in. Its shipping examples also use cm or in; submit all three shipping dimensions together and use a consistent unit. If your source uses millimetres or metres, convert before export. Consult the linked destination rules for limits and shipping setup—the checker above does not validate a complete feed.
| Measurement | Product field | Shipping-package field |
|---|---|---|
| Length | product_length | shipping_length |
| Width | product_width | shipping_width |
| Height | product_height | shipping_height |
Source: Google Merchant Center: Product dimensions and weight; Google Merchant Center: Shipping dimensions
Inches, centimetres, millimetres, and metres: conversion reference
One inch is exactly 25.4 mm or 2.54 cm. One centimetre is 10 mm; one metre is 1000 mm. Apply the same conversion to each labelled axis without swapping length, width, or height. The examples below are arithmetic illustrations, not measurements of a real product.
| From | To | Example |
|---|---|---|
| inches | centimetres: multiply by 2.54 | 24 in = 60.96 cm |
| inches | millimetres: multiply by 25.4 | 24 in = 609.6 mm |
| centimetres | millimetres: multiply by 10 | 60.96 cm = 609.6 mm |
| metres | millimetres: multiply by 1000 | 0.6096 m = 609.6 mm |
Source: NIST: SI units — length
24 inches and 60.96 centimetres can describe the same length
The inch is exactly 25.4 millimetres. In this fictional example, a record contains length 24 in, width 12 in, and height 30 in. Another record contains 60.96 cm, 30.48 cm, and 76.2 cm on those same named axes. Both normalize to 609.6 mm, 304.8 mm, and 762 mm.
That arithmetic says nothing about how accurately the item was measured. Preserve the original precision and source. If an export rounds the length to 61 cm, it differs by 0.4 mm from the supplied 24 in value. An explicitly supplied 0.5 mm comparison tolerance allows that difference; zero tolerance does not. Neither choice is a manufacturing or installation tolerance.
Download the runnable fictional comparison (JSON)Source: NIST: SI units — length; NIST: Writing with SI units
Run the comparison locally
Download the runner and example into one directory, then run node compare-product-dimensions.mjs product-dimensions-example.json with Node.js 18 or later. The script reads the supplied JSON and prints a result. It makes no network requests and does not change either record.
The input has schemaVersion 1.0, source, candidate, and toleranceMm. Each record requires itemId, basis (product or package), evidenceRef, and named length, width, and height objects. Each measurement has value as a positive decimal string and unit as mm, cm, m, or in. Values support up to six decimal places and at most 1000000 units; toleranceMm uses the same decimal format and may be zero. Unknown fields are held for review.
The checker uses integer arithmetic for conversion and comparison. It does not swap axes, parse a range, guess a missing unit, fetch evidence, or check Merchant Center limits. A source reference records where someone should look; its presence does not authenticate the measurement.
| Result | Meaning | CLI exit code |
|---|---|---|
| match | All named dimensions agree within the supplied tolerance and the recorded item/basis agree. | 0 |
| mismatch | At least one comparable dimension exceeds the supplied tolerance. | 1 |
| hold | The input is incomplete, unsupported, or describes a different item or measurement basis. | 2 |
Test conversion, ambiguity, and rounding separately
The ten authored cases include equivalent units, a changed height, product/package confusion, different item IDs, a missing unit, swapped axes, a missing axis, explicit rounding tolerance, zero tolerance, and a range. Each contains the full input, expected status, and reason. Copy a case’s input object into a JSON file to run it individually.
These cases demonstrate the local comparison rules. They are not observed merchant errors or an AI accuracy benchmark. Use additional cases from your own catalog before relying on the checker in a release process.
Download ten inputs and expected decisions (JSON)Fix the source, then inspect the destination
For a mismatch, keep the exact axis, both normalized values, difference, tolerance, and evidence references in the review record. Ask the source owner whether the problem is measurement basis, orientation, rounding, or a wrong value. Do not increase the tolerance simply to make an unexplained difference pass.
After a justified correction, rerun the comparison and check the actual exported field and selected product page. A correct conversion attached to the wrong variant is still unusable.
See what happened with 30 public product listings
The country-page audit preserves real observed measurements alongside retrieval and axis gaps. It separates exact equality from a preselected display-comparison threshold and publishes all sampled records.
Sources & scope
Primary references checked for this edition. The notes below distinguish source-backed facts from the frameworks and examples proposed in this guide.
- Google Merchant Center: Product dimensions and weight ↗
Product measurements, accepted units, and consistent dimension units. The local checker is a separate editorial tool, not a full destination validator.
Checked September 24, 2026 - Google Merchant Center: Shipping dimensions ↗
Package dimensions for carrier-calculated shipping; distinct from the product itself.
Checked September 24, 2026 - NIST: SI units — length ↗
Defines the inch as exactly 25.4 millimetres. Conversion cannot improve the original measurement.
Checked September 24, 2026 - NIST: Writing with SI units ↗
Explains preserving meaningful precision in conversions. The example tolerances are supplied scenario assumptions.
Checked September 20, 2026
AI-assisted research and drafting. Provider-specific claims link to primary sources. Frameworks are editorial proposals; worked examples are illustrative and are not employer performance results.
Editorial policy & corrections ↗Cite this guide
George Kelly. Product dimensions vs package dimensions: compare units safely iamgeorgekelly. Updated September 24, 2026. https://www.iamgeorgekelly.com/field-guide/product-dimensions-unit-conversion
Keep the source notes and example labels with an excerpt. For a provider requirement, follow the original documentation in Sources & scope.