Convert Miles per Hour to Kilometers per Hour – Speed Converter

This converter transforms a single speed value in miles per hour (mph) into kilometres per hour (km/h). It is intended for everyday use such as travel planning, vehicle dashboard checks, and quick unit verification.

The tool applies the internationally accepted relationship between the mile and the metre so results are consistent with national and international standards. For engineering, legal, or safety-critical uses, consider device calibration, measurement uncertainty, and the rounding rules required by the applicable authority.

Updated Nov 3, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 37da952f6178 • Reviewed by Fidamen Standards Committee

Interactive converter unavailable for this calculator.

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Methodology

The conversion is based on the international definition of the mile as exactly 1 609.344 metres and the kilometre as exactly 1 000 metres. Therefore the mathematical factor is exact: 1 mile = 1.609344 kilometres.

Although the numerical conversion factor is exact by definition, the overall accuracy of any measured speed depends on the measurement system, sampling method, and calibration. Follow guidance from standards bodies for traceability: consult NIST for unit definitions, ISO 80000 for quantities and units, IEEE resources for instrumentation and data-quality practices, and OSHA guidance for workplace measurement and calibration where applicable.

Key takeaways

Multiply mph by 1.609344 to get km/h. The factor is exact by definition, but final reported accuracy depends on measurement quality and rounding rules.

Use calibration procedures and follow relevant standards when converting values used for regulatory, engineering, or safety decisions.

Worked examples

1 mph → 1.609344 km/h (exact by definition)

55 mph → 55 × 1.609344 = 88.51392 km/h (display as 88.51 km/h when rounded to two decimals)

60 mph → 60 × 1.609344 = 96.56064 km/h (commonly shown as 96.56 km/h)

F.A.Q.

Why is the factor 1.609344 used?

The factor comes from the international definition of the mile as exactly 1 609.344 metres and the kilometre as 1 000 metres. The factor is therefore exact and standardized.

Is the conversion factor exact or approximate?

The conversion factor 1.609344 is exact given the defined values of the mile and kilometre. Any uncertainty in a converted number arises from how the original speed was measured and from rounding.

How many decimals should I show?

For general use 2 decimal places are often adequate. For engineering, legal, or research contexts follow the precision rules specified by the governing standard or your organisation's measurement policy.

Does this tool account for instrument calibration or measurement error?

No. This converter performs a pure mathematical conversion. Account for instrument calibration, sensor latency, sampling method, and systematic errors separately when reporting measurement results.

Can I convert km/h back to mph?

Yes. To convert km/h to mph divide by 1.609344 (mph = km/h ÷ 1.609344).

Sources & citations

NIST — Definition of the mile (United States customary units reference) — https://physics.nist.gov/cuu/Units/mile.html
ISO 80000 — Quantities and units (overview and purchase page) — https://www.iso.org/standard/30669.html
IEEE Standards Association — Standards and guidance for measurements and instrumentation — https://standards.ieee.org/
OSHA — General guidance on measurement, calibration and workplace instruments — https://www.osha.gov/
BIPM — The International System of Units (SI Brochure) — https://www.bipm.org/en/publications/si-brochure
NIST SP 811 — Guide for the Use of the International System of Units — https://www.nist.gov/pml/special-publication-811

Further resources

Related tools

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: 37da952f6178

What changed (latest)

v1.0.0 • 2025-11-03 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

Governance

Last updated: Nov 3, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
MINOR: New features or fields that do not change existing outputs for the same inputs.
PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

Verify formulas and unit definitions against primary standards or datasets.
Run golden-case regression suite and edge-case suite.
Record reviewer sign-off with credentials and scope.
Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

Uses exact unit definitions from the Fidamen conversion library.
Internal calculations use double precision; display rounding follows the unit's configured decimal places.
Not a substitute for calibrated instruments in regulated contexts.
Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-03 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 678e6bd2c32c