Learn Hardcore Korean: oneul ondoga 30doyeyo. - The temperature today is 30 degrees.

온도 means temperature in a general sense (it can refer to the temperature of any object). 기온 specifically means air temperature or the outdoor temperature you feel when you go outside. In weather reports, 기온 is more common, but 온도 works just as well.

What is the role of the particle -가 in 온도가?

The particle -가 marks 온도 as the subject of the sentence. It indicates that 온도 (temperature) is what is being described as 30 degrees. If you used -는 instead (온도는), you’d be marking it as the topic, which can add a nuance of contrast or known information.

Why is the number 30 pronounced 삼십 instead of 서른?

Because with counters like 도 (degree), Korean uses Sino-Korean numbers (일, 이, 삼…). 삼십 is the Sino-Korean word for 30. 서른 is the native Korean number for 30, used in contexts like age or counting objects, but not with counters.

What does the 도 after 30 represent?

The 도 here is a counter meaning degree (as in degrees of temperature). So 30도 literally means 30 degrees.

Should there be a space between 30 and 도?

No. In Korean, Sino-Korean numerals and their counters are written together without a space: 30도.

Why is -예요 used instead of -입니다 at the end of the sentence?

Both -예요/-이에요 and -입니다 are polite endings. -예요 is polite-casual and commonly used in everyday conversation. -입니다 is more formal and often used in presentations, announcements, or very formal writing.

Can I replace the subject marker -가 with the topic marker -는 (오늘 온도는 30도예요)? How would the nuance change?

Yes, you can say 오늘 온도는 30도예요. Using -는 makes 오늘 온도 the topic, suggesting you’re commenting on it in contrast to something else (like other days or expectations). Using -가 simply presents it as new information without that contrast.

How do I specify whether it’s Celsius or Fahrenheit?

Prefix the temperature with 섭씨 for Celsius or 화씨 for Fahrenheit. For example:
• 섭씨 30도예요 (It’s 30 degrees Celsius.)
• 화씨 86도예요 (It’s 86 degrees Fahrenheit.)