Clean and format phone numbers in a spreadsheet
To clean phone numbers in a CSV, open the phone-number cleaner in Sigmera, pick the default country for numbers that lack a code, and Sigmera normalizes the phone column to the E.164 standard (+14155550100). Preview the formatted numbers, then download the cleaned file. Everything runs in your browser — your data is never uploaded, so it’s GDPR-safe by design.
Last updated: June 2026
Use the phone-number cleaner free in your workspace
Free account, no credit card — every tool, unlimited rows, 3 free downloads a month, nothing uploaded.
🔒 Everything runs in your browser — your file is never uploaded, and the workspace even works offline once it has loaded.
Ways to format phone numbers, compared
| Method | Data uploaded? | Handles E.164 | Skill needed |
|---|---|---|---|
| Sigmera (this tool) | No — runs in browser | Yes, automatically | None |
| Excel formulas | No | Only via nested formulas | High (formulas) |
| Manual editing | No | Error-prone | Low (but slow) |
| Python / phonenumbers | No | Yes | High (code) |
How to clean phone numbers
- 1. Drop your CSV into the tool. The file is read into your browser’s memory — it is never sent over the network. Sigmera auto-detects the phone column.
- 2. Pick the default country. Numbers that already start with a plus sign or an international 00 prefix keep their own code; everything else gets the calling code you choose.
- 3. Preview the formatted numbers. See how many numbers were normalized to E.164 and how many were flagged invalid before you commit. You can re-pick the phone column if auto-detect guessed wrong.
- 4. Download the clean file. Create a free account to export the full CSV with phone numbers in E.164 format.
Why format to E.164 client-side?
E.164 is the ITU international numbering standard — a plus sign, the country calling code, then the national number, with no spaces or punctuation. CRMs, SMS gateways, and dialers reject inconsistent formats, so a single column of mixed numbers breaks imports. Most online formatters fix this by uploading your contact list to a server you can’t see. Because Sigmera processes the file locally with the browser’s built-in JavaScript engine, there is no server to upload to and nothing is stored — which satisfies GDPR data-minimization (Article 5) because zero bytes leave the device.
Frequently asked questions
- Does this tool upload my CSV file?
- No. The phone-number formatter runs entirely inside your web browser using client-side JavaScript. Your file is never uploaded to a server and never leaves your device, so it is GDPR-safe by design.
- What is the E.164 phone format?
- E.164 is the international telephone numbering standard published by the ITU. An E.164 number starts with a plus sign and the country calling code, followed by the national number, with no spaces, dashes, or parentheses — for example +14155550100. It is the format CRMs, SMS APIs, and dialers expect.
- What about numbers without a country code?
- Pick a default country before running. Any number that has no leading plus sign and no international 00 prefix is treated as a national number: Sigmera strips a single leading trunk zero and prepends the calling code you selected, producing a valid E.164 number.
- Can I do this in Excel instead?
- Yes, but it is painful. Excel has no built-in E.164 formatter, so you stack SUBSTITUTE, TEXT, and CONCAT formulas to strip symbols and add the country code, and numbers stored as text break easily. Sigmera normalizes a whole column to E.164 in two clicks without writing a formula.