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Temperature Converter

Measurement

Free online temperature converter. Convert between Celsius, Fahrenheit, Kelvin, and Rankine instantly. Covers body temperature, oven settings, and weather conversions.

From
To

What is a Temperature?

A temperature converter translates readings between the world's temperature scales — Celsius (°C), Fahrenheit (°F), Kelvin (K), and Rankine (°R). Temperature conversion is more complex than most unit conversions because scales differ not only in unit size but also in where they place zero: Celsius and Fahrenheit are relative scales (zero is not the coldest possible temperature), while Kelvin and Rankine are absolute scales anchored at absolute zero.

India uses Celsius exclusively for weather forecasts, medicine, and everyday conversation. The United States uses Fahrenheit for weather and cooking. Science and engineering globally use Kelvin for thermodynamics and physics. When a temperature from one context appears in another — an American oven recipe in Fahrenheit, a medical reference from the UK, a physics textbook using Kelvin — the conversion must handle both the scale factor and the offset correctly.

Temperature context matters significantly in India. A 45°C day in Delhi in June is a severe heat event; expressing it as 113°F helps communicate that severity to international colleagues. A fever of 102°F on an imported thermometer means 38.9°C — just above the 38°C threshold for fever medication in Indian paediatric guidelines. These conversions have real consequences.

For recipe work alongside temperature, the Volume Converter handles US cups and fluid ounces, and the Area Converter covers property measurements if you are working across mixed-unit documents.

How to use this Temperature calculator

  1. Enter the temperature value in the FROM field. Negative values are valid — Celsius and Fahrenheit frequently go below zero.
  2. Select the FROM scale — Celsius, Fahrenheit, Kelvin, or Rankine.
  3. Select the TO scale for your target measurement.
  4. Read the result instantly in the TO field. The reference table below shows all four scales simultaneously.
  5. Type in the TO field to reverse-convert — enter the target temperature and the FROM field back-calculates.
  6. Swap — the ⇅ button reverses FROM and TO while preserving the entered value.

Formula & Methodology

Temperature conversion is non-linear. The converter routes all conversions through Celsius as an intermediate step:

Celsius ↔ Fahrenheit:
- °F = (°C × 9/5) + 32
- °C = (°F − 32) × 5/9

Celsius ↔ Kelvin:
- K = °C + 273.15
- °C = K − 273.15

Celsius ↔ Rankine:
- °R = (°C + 273.15) × 9/5
- °C = (°R − 491.67) × 5/9

All other scale combinations (e.g. Fahrenheit to Kelvin) convert to Celsius first, then to the target scale.

Common reference temperatures:

| Description | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | −273.15°C | −459.67°F | 0 K |
| Water freezes | 0°C | 32°F | 273.15 K |
| Normal body temp | 37°C | 98.6°F | 310.15 K |
| Fever threshold | 38°C | 100.4°F | 311.15 K |
| Water boils | 100°C | 212°F | 373.15 K |
| Delhi peak summer | 45°C | 113°F | 318.15 K |

Worked example — interpreting a fever reading:

A child's temperature is recorded as 103°F on an imported US thermometer. Converting to Celsius:

°C = (103 − 32) × 5/9 = 71 × 5/9 = 39.44°C

This is significantly above the 38°C fever threshold, and above the 39°C level that warrants prompt medical evaluation in most Indian paediatric guidelines. The conversion changes the clinical picture from an ambiguous Fahrenheit number to a clearly actionable Celsius reading.
Frequently Asked Questions
What is a temperature converter?
A temperature converter translates temperature readings between different scales — Celsius, Fahrenheit, Kelvin, and Rankine. Unlike most unit conversions, temperature scales differ in both their unit size and their zero point, so the conversion requires both multiplication and addition rather than a simple factor. The converter handles the full formula automatically for any scale combination.
What is the formula to convert Celsius to Fahrenheit?
To convert Celsius to Fahrenheit, multiply by 9/5 and add 32: °F = (°C × 9/5) + 32. For example, 100°C = (100 × 1.8) + 32 = 212°F. To reverse, subtract 32 then multiply by 5/9: °C = (°F − 32) × 5/9.
What is 37°C in Fahrenheit?
37°C converts to exactly 98.6°F — the classic normal human body temperature. A reading of 37.5°C (99.5°F) or above is typically considered a low-grade fever in adults, while 38°C (100.4°F) and above is classified as fever by most medical guidelines used in India.
What is 100°F in Celsius?
100°F equals approximately 37.78°C. In weather terms, a 100°F summer day — common in Rajasthan and parts of UP during May and June — represents a severe heat event. India's IMD reports temperatures in Celsius, so this conversion helps when comparing Indian and US weather reports or news coverage.
At what temperature are Celsius and Fahrenheit equal?
Celsius and Fahrenheit are equal at −40°. Both scales read −40 at that exact point, making it a useful mental anchor for understanding how the two scales relate. Below −40 the Fahrenheit number is smaller than the Celsius number; above −40 Fahrenheit is always the larger number.
What is the difference between Celsius and Fahrenheit?
Celsius defines 0° as water's freezing point and 100° as its boiling point, giving a 100-degree span across the water phase change. Fahrenheit defines 32° as freezing and 212° as boiling, a 180-degree span. One Celsius degree therefore represents 1.8 Fahrenheit degrees of temperature change.
What is normal body temperature in Celsius and Fahrenheit?
Normal adult body temperature is typically cited as 37°C (98.6°F), but the normal range is 36.1°C to 37.2°C (97°F to 99°F) depending on time of day and measurement method. Indian paediatric guidelines generally define fever as 38°C (100.4°F) or above, which corresponds to 100.4°F.
What is the boiling point of water in Fahrenheit?
Water boils at 212°F (100°C) at standard atmospheric pressure at sea level. At higher altitudes — such as Shimla at 2,200 m or Leh at 3,500 m — reduced air pressure lowers the boiling point to approximately 92°C and 87°C respectively, which increases cooking times for boiled and steamed foods.
What is Kelvin and when is it used?
Kelvin is the SI base unit for temperature, starting at absolute zero (−273.15°C), the coldest theoretically possible temperature. Unlike Celsius and Fahrenheit, Kelvin has no negative values. It is used in physics, chemistry, astrophysics, and engineering where absolute temperature matters — thermodynamics calculations, blackbody radiation, and cryogenic systems all require Kelvin.
What is absolute zero in Celsius and Fahrenheit?
Absolute zero is 0 Kelvin, which equals −273.15°C or −459.67°F. This is the theoretical minimum temperature at which all molecular motion ceases. It has never been achieved experimentally, though laboratories have reached within billionths of a degree of it.
How do I mentally convert Celsius to Fahrenheit?
A quick approximation: double the Celsius temperature and add 30. For example, 25°C → (25 × 2) + 30 = 80°F (actual: 77°F). This slightly overestimates but is accurate enough for weather conversation. For body temperature, remembering that 37°C = 98.6°F and 38°C = 100.4°F gives reliable clinical reference anchors.
What is 0°C in Fahrenheit?
0°C equals 32°F — the freezing point of water. Any Fahrenheit reading below 32 means below-freezing conditions. Sub-zero Celsius temperatures occur in Ladakh, Himachal Pradesh, and Uttarakhand during winter months, reaching −20°C (−4°F) or below in Leh.

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