Best Free Online Converters 2026: Units, Temperature, Binary, Roman & More
From converting miles to kilometers for a trip, to flipping binary for a school project, to decoding a Unix timestamp from an API log — converters are the quiet workhorses of the internet. The best free online converters handle all of it instantly, with no installs, no signups, and nothing sent to a server.
The free converters we recommend
| Task | Free tool | Why it wins |
|---|---|---|
| Any unit | Unit Converter | Length, weight, temperature, volume — everything in one box |
| Temperature | Celsius to Fahrenheit | Instant °C ↔ °F with the formula shown |
| Text ⇄ binary | Text to Binary | Both directions, live as you type |
| Binary ⇄ text | Binary to Text | Decode binary strings back to readable text |
| Roman numerals | Roman Numeral Converter | Numbers ⇄ Roman, both ways |
| Unix timestamps | Timestamp Converter | Unix ↔ human dates for logs and APIs |
| Base64 | Base64 Encode/Decode | Encode and decode strings for APIs and tokens |
| Number to words | Number to Words | Amounts in words for checks and invoices |
Why browser-based converters
- Instant — results update as you type, both directions
- Accurate — no mental-math rounding errors
- Private — your input never leaves your device
- Free forever — no freemium walls, no daily limits
Business use: convert data, not just units
For accountants and bookkeepers, the most valuable "converter" is the one that turns bank statement PDFs into CSV — that's BankToCSV, purpose-built for QuickBooks and Xero imports. Pair it with InvoiceForge for billing and you've got the paperwork side of a small business covered.
Open Unit Converter
Frequently Asked Questions
Are these converters really free? Yes — unlimited use, no account, no watermark, no rate limits.
Is my data uploaded? No. Every converter runs in your browser, so your input never leaves your device.
Which converter handles bank statements? That's BankToCSV — it converts statement PDFs from major banks into CSV for accounting software.
Do these work on mobile? Yes — all converters are fully responsive and work on any device.