Why SKUs lose leading zeros in CSV files

A SKU is an identifier, even when it contains only digits. Leading zeros can be part of that identifier. CSV files store text values separated by delimiters, but they do not carry column types that tell a spreadsheet application, “This column must remain text.” The application may therefore interpret a SKU as a number.

Synthetic example: 00123 → 123. This invented example illustrates numeric interpretation; it is not a customer file or a completed test. A spreadsheet may show 123 after reading the original value 00123. That display alone does not prove that the original CSV has changed. Simply opening a file does not necessarily overwrite it. Saving or exporting the interpreted data can write the shortened value into a new or existing file.

Preserve the original before editing. Keep an untouched copy of the original CSV and work on a separate copy. Before importing, inspect the original SKU values in a plain text viewer that does not convert numeric strings. This gives you a reference for comparison. Avoid using another spreadsheet opening as your reference: it may apply the same automatic conversion.

Import the SKU column as text. Use your spreadsheet application’s text or CSV import workflow, where you can choose how columns are interpreted. Set the SKU column to Text before completing the import. If the workflow offers automatic type detection, disable it for that column. Menu names vary between applications, so look for column type or conversion settings in the import preview. Check that leading zeros remain visible before editing.

Formatting after conversion cannot recover the original. Changing a cell to Text after its value has become 123 does not restore 00123. Likewise, a display format that shows five digits can make 123 look like 00123 without restoring the original identifier. Appearance is not proof of the underlying value. Do not add zeros based on a guessed SKU length: identifiers can have different lengths, and guessing can create the wrong product reference.

Compare the exported values. Export your working copy to a separate CSV. Open that export in a plain text view without numeric conversion, and compare its SKU field values with the verified original. For the synthetic example, the exported field should still contain 00123. CSV quotation marks alone do not reliably prevent spreadsheet applications from interpreting a value as numeric when it is reopened.

If zeros have already been lost, restore them only from a verified original file or an authoritative product record. Without that evidence, the correct identifier remains uncertain.

Want another check before using your product file? Try the free CSV check. It does not replace comparison with your original source; do not assume it can automatically detect or repair missing leading zeros.