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.

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Last verified July 2026

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Direct answer

What does this converter do?

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.

  • 1 mph = 1.609 km/h · 1 knot = 1.852 km/h · 1 km/h = 0.2778 m/s
  • All conversions route through the m/s as the base unit, so every pair of units agrees regardless of which two you enter.
  • Standard factors are shown in the formula panel at the precision the calculator actually uses, so the arithmetic and the panel agree.
Speed units compared: mph, km/h, knots, and meters per second
The mile is exactly 1,609.344 meters, so speed conversions are exact.

Reference factors (speed)

Exact factors in terms of the m/s, from NIST standards:

  • 1 km/h = 0.277778 m/s
  • 1 ft/s = 0.3048 m/s
  • 1 mph = 0.44704 m/s
  • 1 knot = 0.514444 m/s
  • 1 m/s = 1 m/s
Formula & evidence

How this calculator works

Reviewed 2026-09-20 · BoringToolsKit Editorial Team

Formula

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

Sources

Sources support the method, terminology, or planning context. Editable assumptions remain your responsibility.

Assumptions to verify

  • 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.

Frequently asked 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.

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Cite this tool

BoringToolsKit. “Speed Converter.” boringtoolskit.com/speed-converter/ (reviewed 2026-09-20). Free to reference in articles, syllabi, and answer posts with a link.

Privacy: Inputs and results stay in this browser. Conversion runs locally in your browser; review the output before relying on it.

Worked example: 65 mph to metres per second

Set the value to 65, the from-unit to mph and the to-unit to m/s. The script first converts the input to metres per second using the factor 0.44704, which is exact: one mile is 1609.344 metres and one hour is 3600 seconds, so 1609.344 / 3600 = 0.44704 exactly. The multiplication gives 65 x 0.44704 = 29.0576 m/s. No division is needed on the way out because the target unit is already m/s (factor 1), so the display rounds 29.0576 to 29.06 m/s.

The same input run the other direction confirms the arithmetic: 29.0576 / 0.44704 = 65.0. For a metric-to-metric check, 100 km/h becomes 100 x 0.2777778 = 27.77778 m/s, and dividing by 0.44704 gives 62.14 mph, matching the familiar 1.609344 km per mile. If you want knots, 15 knots is 15 x 0.5144444 = 7.716666 m/s, and 7.716666 / 0.44704 = 17.26 mph, which is the 1.1508 ratio the result box quotes.

Where the rounding shows up

Two factors in the table are rounded, not exact. The km/h entry is 0.2777778 instead of the exact 1/3.6 = 0.2777777778, and the knot entry is 0.5144444 instead of the exact 1852/3600 = 0.51444444. For 100 km/h the rounded factor returns 27.77778 m/s versus 27.777778 exact, a difference of about 0.000002 m/s, far below the two-decimal display. Even at 25,000 km/h, re-entry speed territory, the gap is under 0.0006 m/s, so it never changes a displayed digit.

What can move a displayed digit is the output formatter: values under 1 get four significant figures, values 1 to 999 get two decimals, and 1,000 or above drops to whole numbers with comma separators. Convert 12,000 ft/s to mph and you get 8,182 mph, not 8,181.8. Also note the input gate: a value of 0 or a negative number is rejected rather than returned as 0, so the converter cannot express a standstill, and pasting a value with a comma or unit text yields 0 and triggers the same rejection.