Convert Fahrenheit to Celsius – Temperature Converter

This tool converts a single temperature value from degrees Fahrenheit (°F) to degrees Celsius (°C) using the exact linear relationship between the two scales. It is intended for everyday conversions, engineering checks, and documentation where a reliable numeric translation is required.

Conversions returned are mathematical results; for measurements taken with instruments, review instrument specification sheets and calibration records. For precision-critical work (laboratory calibration, regulatory reporting, process control), follow recognized standards and calibration procedures rather than treating the conversion alone as a measurement assurance step.

Updated Nov 13, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 7e9010beedd0 • Reviewed by Fidamen Standards Committee

Interactive Converter

Convert between fahrenheit and celsius with precision rounding.

Fahrenheit (°F)Celsius (°C)

Quick reference table

Fahrenheit	Celsius
1 °F	-17.22 °C
5 °F	-15 °C
10 °F	-12.22 °C
25 °F	-3.89 °C
50 °F	10 °C
100 °F	37.78 °C

Methodology

The Fahrenheit-to-Celsius conversion is a fixed linear transformation derived from the definition of the two temperature scales. The converter applies the exact arithmetic formula Celsius = (Fahrenheit − 32) × 5/9. This is an exact rational conversion and does not approximate the relationship.

While the arithmetic conversion is exact, real-world measurement accuracy depends on instrument performance, calibration traceability, and measurement uncertainty. Follow NIST guidance on temperature scales (ITS-90) and ISO/IEC 17025 requirements for calibration laboratories when traceability or documented uncertainty is required. For workplace or safety thresholds consult applicable OSHA guidance.

Worked examples

32 °F → (32 − 32) × 5/9 = 0 °C

212 °F → (212 − 32) × 5/9 = 100 °C

-40 °F → (-40 − 32) × 5/9 = -40 °C

F.A.Q.

Is the conversion formula exact or approximate?

The formula °C = (°F − 32) × 5/9 is an exact linear relationship between the two scales. Any difference you see is due to rounding for display, not the formula itself.

How many decimal places should I use for reporting?

Choose decimal precision based on context and instrument uncertainty. Typical practical reporting is 0.1 °C for weather data, 0.01 °C or better for laboratory work if instruments support that precision. Always align reported precision with measured uncertainty from calibration certificates (ISO/IEC 17025).

Does this tool compensate for instrument calibration or measurement error?

No. This converter performs only the mathematical unit conversion. For calibrated measurements, apply instrument corrections and uncertainty budgets from calibration records before or after conversion as appropriate.

Can I convert negative temperatures and values below freezing?

Yes. The formula applies across the full numeric range of the two scales, including negative values and extremes approaching absolute zero. For temperatures near absolute zero, ensure your instruments and procedures are appropriate.

How does this relate to Kelvin?

To convert Fahrenheit to Kelvin, first convert Fahrenheit to Celsius with this formula, then add 273.15 to convert Celsius to Kelvin. Kelvin is the SI base unit for thermodynamic temperature.

Sources & citations

NIST — International Temperature Scale of 1990 (ITS-90) — https://www.nist.gov/programs-projects/international-temperature-scale-1990-its-90
ISO/IEC 17025 — General requirements for the competence of testing and calibration laboratories — https://www.iso.org/standard/66912.html
OSHA — Heat Stress and Heat-Related Illnesses guidance — https://www.osha.gov/heat-exposure
IEEE Instrumentation & Measurement Society — https://ieee-ims.org/
ISO 80000-5:2019 — Thermodynamics — https://www.iso.org/standard/64976.html
NIST SP 330 — The International System of Units (SI) — https://www.nist.gov/pml/special-publication-330
BIPM SI Brochure (9th edition, 2019) — https://www.bipm.org/en/publications/si-brochure

Further resources

Related tools

External guidance

Versioning & Change Control

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

Record ID: 7e9010beedd0

What changed (latest)

v1.0.0 • 2025-11-13 • 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 13, 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 • 2025-11-13 • 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: ca085432ff1c