How to Use This Tool
Converting temperature looks like the simplest unit conversion there is, and it contains one genuine trap that catches scientists, engineers and cooks alike. Length, weight and volume all scale from a shared zero, so converting them is a single multiplication. Temperature scales do not share a zero, which is why Fahrenheit needs that awkward +32 — and why converting a difference follows a different rule from converting a temperature.
Converting a temperature
Leave the mode on A temperature, type a value and choose its scale. All four scales
update at once. The formulas are shown live so you can check the arithmetic rather than trust it:
°F = °C × 9/5 + 32, K = °C + 273.15, and Rankine, which is Fahrenheit's
absolute scale, °R = °F + 459.67.
Two useful mental anchors: −40 is the one point where Celsius and Fahrenheit agree, and 16°C is almost exactly 61°F, which is the easiest digit-reversal pair to remember. For rough conversions in your head, double the Celsius and add 30 — it is within a few degrees across normal weather.
The difference mode, and why it exists
Switch to A difference when your number is a gap rather than a reading: "the temperature rose by 15 degrees", "keep it within 5 degrees", "this component's tolerance is ±10 degrees". In that case the offset must not be applied. A 15°C rise is a 27°F rise, not 59°F. Applying the wrong formula here is a real and expensive error in engineering specifications, HVAC calculations and equipment datasheets, and it is entirely invisible unless someone checks.
Absolute zero and the impossibility check
Kelvin and Rankine start at absolute zero, the point where molecular motion stops, so they can never be negative. If a conversion produces a negative Kelvin value the tool says so rather than printing it, because the input was almost certainly wrong — usually a Fahrenheit value entered as Celsius. Absolute zero is −273.15°C or −459.67°F, and no laboratory has ever reached it.
Everyday reference points
The table at the bottom gives the temperatures people actually look up: fridge and freezer targets, safe cooking temperatures for poultry and beef, fever thresholds, common oven settings, and the boiling point of water — which is 100°C only at sea level, and drops by roughly 1°C for every 300 metres of altitude. That last one matters if you are following a recipe in Denver or Mexico City and wondering why the timings are wrong.