# Speed Converter

> Speed converter converts between mph, km/h, knots, m/s, and ft/s instantly with a quick reference table. Free, private, runs in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/speed-converter/
- **Category:** Converters
- **Evidence level:** authored-methodology
- **Reviewed:** 2026-09-20
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

Speed = value x (metres per second per source unit) / (metres per second per target unit). Factors: 1 mph = 0.44704 m/s, 1 km/h = 0.2777778 m/s, 1 ft/s = 0.3048 m/s, 1 knot = 0.5144444 m/s.

## Worked example

1 mph = 1.609 km/h · 1 knot = 1.852 km/h · 1 km/h = 0.2778 m/s

## Assumptions

- Inputs are treated as exact decimal values.
- Standard (not historical or survey) unit definitions are used.
- The calculation uses the factors at the precision shown in the formula panel; rounding beyond that is display-only and adds no accuracy.

## Common questions

### Why convert through m/s instead of directly?

Routing every unit through a single base (m/s) means each unit needs only one exact factor against the standard, and any pair combines cleanly. Direct pair factors drift apart over time in hand-maintained tables; a base-unit graph cannot.

### Where do these exact factors come from?

From published standards (NIST: SP 811 speed conversions). Units like the inch are defined exactly (1 in = 2.54 cm since 1959), so conversions between standard units are exact, not approximate.

### How precise is the converted speed?

The conversion applies the standard factors shown in the formula panel. The practical limit is your input: the result only regroups the number you entered, so digits beyond your original reading do not add accuracy. 3-4 significant figures usually matches what the source measurement knew.

## Sources

- [SP 811 speed conversions](https://www.nist.gov/pml/special-publication-811)

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