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To convert Kelvin to Celsius, subtract 273.15. So 300 K = 26.85°C (warm room), 273.15 K = 0°C (water freezing), and 0 K = −273.15°C (absolute zero). Kelvin is always positive; if you subtract 273.15 and get a negative result, that is simply a temperature below water's freezing point.
Scientific literature, textbooks, and lab reports use Kelvin because it is the SI thermodynamic unit. When real-world interpretation is needed — is 350 K hot enough to bake bread? (76.85°C — no) — converting back to Celsius provides immediate intuitive context. The Sun's photosphere at 5,778 K = 5,504.85°C.
Did you know? The cosmic microwave background radiation — the afterglow of the Big Bang — has a temperature of 2.725 K, or about −270.4°C. This is one of the coldest measured temperatures in the known universe (discounting laboratory extremes).
Reading scientific papers and translating results to everyday temperature ranges. Chemistry students learning thermodynamics who want to check whether calculated temperatures make physical sense. Astronomy enthusiasts interpreting stellar classification temperatures in relatable Celsius terms. Any engineer checking whether a computed operating temperature falls within a practical range.