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Fahrenheit to Celsius Calculator

Convert a temperature from Fahrenheit to Celsius for metric specifications and datasheets.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Temperature

70 °F

High confidence

°C = (°F − 32) × 5/9. The offset makes this affine, not a simple multiplier. Temperature differences convert with the 5/9 ratio only — never apply the 32-degree offset to a delta-T.

Datasheets, cure schedules and equipment ratings cross this boundary constantly, and the conversion is unlike the others on this site because the two scales do not share a zero. That offset is what makes it affine rather than a simple multiplier, and it is also the source of the mistake that matters. A temperature converts one way; a temperature difference converts another. A ten-degree Fahrenheit rise is a 5.6 degree Celsius rise, obtained with the five-ninths ratio alone — applying the thirty-two degree offset to a difference produces a figure that is not merely wrong but absurd, and heat-loss calculations built on delta-T are exactly where this goes unnoticed. Minus forty, where both scales coincide, is a quick sanity check.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Celsius = (Fahrenheit - 32) x 5/9; the scales share a value at -40 degrees

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Does this work for a temperature difference?
No, and this is the important caveat. A difference converts with the 5/9 ratio alone: a 10°F rise is a 5.6°C rise. Applying the 32-degree offset to a difference produces a nonsensical answer and will wreck a heat-loss calculation.
Is there a temperature where both scales agree?
Minus forty. −40°F and −40°C are the same temperature, which makes it a handy check that a conversion has been done correctly.
Why does concrete work specify temperature so tightly?
Because hydration rate depends strongly on it. Cold slows strength gain and risks freezing before set; heat accelerates setting and raises evaporation, which drives plastic shrinkage cracking. Both ends of the range have their own published precautions.