Photo: Jarosław Kwoczała / Unsplash
What’s the Difference and Why Are There So Many Temperature Scales
Temperature is one of the most familiar quantities in our lives. We check it before leaving the house, look at the weather forecast, and talk about heat or frost. But when you open a foreign website or a scientific article, you encounter Fahrenheit, Kelvin, Rankine, and even Réaumur. Why are there so many temperature scales and how do they differ?
Celsius Scale (°C) — the Most Familiar
The Celsius scale is used in most countries worldwide and is perfect for everyday life.
Its logic is simple:
- 0°C — freezing point of water
- 100°C — boiling point of water (at normal pressure)
Thanks to this, the scale is intuitively clear: negative values mean cold, positive values mean warmth.
Fahrenheit Scale (°F) — the Choice of the USA
Fahrenheit is used in the USA and some other countries. Here, things look less obvious:
- 32°F — freezing point of water
- 212°F — boiling point of water
The advantage of the Fahrenheit scale is that it is more “detailed”: one degree is smaller than a degree Celsius, so temperature changes seem smoother.
Kelvin Scale (K) — the Basis of Science
Kelvin is an absolute temperature scale used in physics, chemistry, and engineering.
Main features:
- 0 K — absolute zero, the lowest possible temperature in the Universe
- There are no negative values
One kelvin is equal in size to one degree Celsius, but the scale starts not from the freezing point of water, but from absolute zero.
Rankine Scale (°R) — Rare but Logical
Rankine combines ideas from Fahrenheit and Kelvin:
- Zero of the scale is absolute zero
- The degree size equals the Fahrenheit degree
It is mainly used in engineering calculations in the USA, especially in thermodynamics.
Réaumur Scale (°Ré) — a Historical Rarity
Réaumur is one of the oldest temperature scales, almost unused today.
Features:
- 0°Ré — freezing point of water
- 80°Ré — boiling point of water
Sometimes it can be found in old European sources or historical documents.
Temperature Conversion Formulas
To avoid confusion, here are the most important formulas:
Celsius ↔ Fahrenheit
- °F = °C × 9/5 + 32
- °C = (°F − 32) × 5/9
Celsius ↔ Kelvin
- K = °C + 273.15
- °C = K − 273.15
Fahrenheit ↔ Rankine
- °R = °F + 459.67
- °F = °R − 459.67
Celsius ↔ Réaumur
- °Ré = °C × 4/5
- °C = °Ré × 5/4
Why It’s Important to Understand Different Scales
Different temperature scales exist for good reasons:
- Celsius — for everyday life and weather
- Fahrenheit — for daily use in the USA
- Kelvin — for science and precise calculations
- Rankine — for engineering
- Réaumur — part of the history of science
Understanding the differences helps to navigate international weather forecasts, scientific publications, and technical documentation more easily.
Comparative Table of Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur Temperature Scales
| Celsius (Celsius) |
300.00 | 290.00 | 280.00 | 270.00 | 260.00 | 250.00 | 240.00 | 230.00 | 220.00 | 210.00 | 200.00 | 190.00 | 180.00 | 170.00 | 160.00 | 150.00 | 140.00 | 130.00 | 120.00 | 110.00 | 100.00 | 90.00 | 80.00 | 70.00 | 60.00 | 50.00 | 40.00 | 30.00 | 20.00 | 10.00 | 0.00 | -10.00 | -20.00 | -30.00 | -40.00 | -50.00 | -60.00 | -70.00 | -80.00 | -90.00 | -100.00 | -110.00 | -120.00 | -130.00 | -140.00 | -150.00 | -160.00 | -170.00 | -180.00 | -190.00 | -200.00 | -210.00 | -220.00 | -230.00 | -240.00 | -250.00 | -260.00 | -273.15 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fahrenheit (Fahrenheit) |
572.00 | 554.00 | 536.00 | 518.00 | 500.00 | 482.00 | 464.00 | 446.00 | 428.00 | 410.00 | 392.00 | 374.00 | 356.00 | 338.00 | 320.00 | 302.00 | 284.00 | 266.00 | 248.00 | 230.00 | 212.00 | 194.00 | 176.00 | 158.00 | 140.00 | 122.00 | 104.00 | 86.00 | 68.00 | 50.00 | 32.00 | 14.00 | -4.00 | -22.00 | -40.00 | -58.00 | -76.00 | -94.00 | -112.00 | -130.00 | -148.00 | -166.00 | -184.00 | -202.00 | -220.00 | -238.00 | -256.00 | -274.00 | -292.00 | -310.00 | -328.00 | -346.00 | -364.00 | -382.00 | -400.00 | -418.00 | -436.00 | -459.67 |
| Kelvin (Kelvin) |
573.15 | 563.15 | 553.15 | 543.15 | 533.15 | 523.15 | 513.15 | 503.15 | 493.15 | 483.15 | 473.15 | 463.15 | 453.15 | 443.15 | 433.15 | 423.15 | 413.15 | 403.15 | 393.15 | 383.15 | 373.15 | 363.15 | 353.15 | 343.15 | 333.15 | 323.15 | 313.15 | 303.15 | 293.15 | 283.15 | 273.15 | 263.15 | 253.15 | 243.15 | 233.15 | 223.15 | 213.15 | 203.15 | 193.15 | 183.15 | 173.15 | 163.15 | 153.15 | 143.15 | 133.15 | 123.15 | 113.15 | 103.15 | 93.15 | 83.15 | 73.15 | 63.15 | 53.15 | 43.15 | 33.15 | 23.15 | 13.15 | 0.00 |
| Rankine (Rankine) |
1031.67 | 1013.67 | 995.67 | 977.67 | 959.67 | 941.67 | 923.67 | 905.67 | 887.67 | 869.67 | 851.67 | 833.67 | 815.67 | 797.67 | 779.67 | 761.67 | 743.67 | 725.67 | 707.67 | 689.67 | 671.67 | 653.67 | 635.67 | 617.67 | 599.67 | 581.67 | 563.67 | 545.67 | 527.67 | 509.67 | 491.67 | 473.67 | 455.67 | 437.67 | 419.67 | 401.67 | 383.67 | 365.67 | 347.67 | 329.67 | 311.67 | 293.67 | 275.67 | 257.67 | 239.67 | 221.67 | 203.67 | 185.67 | 167.67 | 149.67 | 131.67 | 113.67 | 95.67 | 77.67 | 59.67 | 41.67 | 23.67 | 0.00 |
| Réaumur (Reaumur) |
240.00 | 232.00 | 224.00 | 216.00 | 208.00 | 200.00 | 192.00 | 184.00 | 176.00 | 168.00 | 160.00 | 152.00 | 144.00 | 136.00 | 128.00 | 120.00 | 112.00 | 104.00 | 96.00 | 88.00 | 80.00 | 72.00 | 64.00 | 56.00 | 48.00 | 40.00 | 32.00 | 24.00 | 16.00 | 8.00 | 0.00 | -8.00 | -16.00 | -24.00 | -32.00 | -40.00 | -48.00 | -56.00 | -64.00 | -72.00 | -80.00 | -88.00 | -96.00 | -104.00 | -112.00 | -120.00 | -128.00 | -136.00 | -144.00 | -152.00 | -160.00 | -168.00 | -176.00 | -184.00 | -192.00 | -200.00 | -208.00 | -218.52 |