The adverb 多 is placed before a monosyllabic adjective to enquire about degree.
多高？How high? How tall?
When we ask “你多大？”, it is to ask the age of other person.
Sometimes, 多大？ can also be used to ask the size, for example,
How big is this clothes?
Zhè jiàn yīfú duōdà?
Therefore, if we want to know the exact meaning of 多大, we shall decide based on the context.
你多高？How tall are you?
Nǐ duō gāo?
我一米七五。I am one point seventy-five meters.
Wǒ yī mǐ qīwǔ.
裤子多长？How long are the trousers?
Kùzi duō cháng?
裤子长一米一。The trousers are one point one meters long.
Kùzi cháng yī mǐ yī.
公司离这儿多远？How far is the company from here?
Gōngsī lí zhè’er duō yuǎn?
公司离这儿五百米。The company is five hundred meters away from here.
Gōngsī lí zhè’er wǔbǎi mǐ.
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