Guide: Unit Converter Online
↑ Back to toolWhat is this tool?
Spoold's free unit converter online converts one number into every related unit in a category—instantly, in your browser. Enter 7 days and see milliseconds, seconds, hours, and weeks in one list. The same pattern works for length (km ↔ miles), mass (kg ↔ lb), data size (MiB ↔ GB), and temperature (°C ↔ °F ↔ K). No sign-up; nothing is uploaded to a server for conversion math.
Unlike a two-box “from / to” calculator that forces you to pick the target unit first, this tool uses a one → many layout: pick the source unit, type the value, and scan or copy any result. That is ideal when you are not sure whether you need ms, µs, or seconds until you see the magnitudes side by side.
Quick tip
Paste Magic Box phrases like 7 days or 100km—the converter opens with category and unit preselected when possible.
Why use an online unit converter?
- API & backend timeouts — Convert days to milliseconds or hours to seconds for Redis TTL, JWT expiry, and cron-adjacent delays without spreadsheet formulas.
- Cross-system specs — Product docs in miles/feet vs SI meters; shipping weights in lb vs kg.
- Storage & networking — Compare SI (kB, MB) and IEC (KiB, MiB) sizes when reading disk quotas or CDN invoices.
- Fast, private — Client-side math; paste sensitive config numbers without sending them to a third-party converter site.
Categories & units supported
| Category | Units |
|---|---|
| Duration | ns, µs, ms, s, min, h, day, week (base: milliseconds) |
| Length | mm, cm, m, km, in, ft, yd, mi (base: meters) |
| Mass | mg, g, kg, oz, lb, metric ton (base: kilograms) |
| Data | bit, B, kB/KiB, MB/MiB, GB/GiB, TB/TiB (base: bytes) |
| Temperature | Celsius, Fahrenheit, Kelvin (formula-based) |
How to use the unit converter
- Choose a category chip (Duration, Length, Mass, Data, or Temperature).
- Type the numeric value. Select the from unit with the dropdown or the short chips (e.g. day, ms, km).
- Scan the Results list. Use Copy for any row, or the swap control to make that unit the new source.
- Optional: filter units by name when a category is long (especially Data).
Days to milliseconds (and other duration conversions)
Duration is the most common engineering use case. Example: 7 days to milliseconds = 604800000 ms (7 × 24 × 60 × 60 × 1000). The converter also shows seconds, minutes, hours, weeks, and finer units (µs, ns) for the same absolute duration.
All duration units share a millisecond base so chaining stays consistent: week → day → hour → minute → second → ms → µs → ns. For calendar dates and Unix epoch values, use the Unix timestamp converter instead—this tool converts spans of time, not clock timestamps.
Length, mass & data size
Length covers metric and imperial (mm through miles). Mass covers mg–ton plus ounces and pounds. Data lists both SI decimal prefixes (kB, MB, GB, TB) and IEC binary prefixes (KiB, MiB, GiB, TiB) so you can see why “1 GB” and “1 GiB” differ when vendors disagree.
Factors follow standard SI / IEC definitions (e.g. 1 inch = 0.0254 m, 1 lb = 0.45359237 kg, 1 MiB = 2²⁰ bytes).
Temperature conversion
Temperature is not a linear scale from a single base factor. Spoold converts via Celsius: °F ↔ °C ↔ K using the usual formulas. Absolute zero is 0 K (−273.15 °C); the tool does not block physically extreme values, so double-check domain meaning for scientific work.
Practical use cases
- Set
maxAge/ cache TTL from “7 days” into ms - Translate map or CAD distances between km and miles
- Reconcile package weight labels (kg vs lb)
- Explain disk usage screenshots that mix GB and GiB
- Quick weather or lab conversions between °C and °F
Frequently asked questions
Is this unit converter free?▾
Yes. It runs entirely in your browser with no account required.
How do I convert 7 days to milliseconds?▾
Open Duration, enter 7, select Days as the from-unit, then copy the Milliseconds row (604800000).
What is the difference between MB and MiB?▾
MB uses 10⁶ bytes (SI); MiB uses 2²⁰ bytes (IEC). Both appear under Data so you can compare.
Can I convert Unix timestamps here?▾
No—use the Unix Timestamp Converter for epoch ↔ date. This tool converts duration lengths, not calendar instants.
Are results exact?▾
Linear categories use standard exact factors. Display may round for readability; copy the formatted value for everyday use, or scale carefully for scientific precision.
Related search terms
Similar tools
- Unix timestamp converter — epoch seconds/ms ↔ human dates
- Number base converter — binary, hex, decimal, radix 2–36
- Cron parser — schedule expressions next to duration planning
Conclusion
Use Spoold's unit converter whenever you need a fast, private days to milliseconds, length, mass, data, or temperature conversion with every related unit visible at once. Bookmark /tools/unit-converter for the next TTL, shipping label, or storage math check.