When you are asked about the quantity or extent of something but you do not know the exact amount or measurements, you could qualify your answer with the help of such words as “about”, “approximately” or “roughly”.
大约 (dàyuē) means roughly or approximately. The formal equivalents are
约略 (yuēlüè rougly, approximately) and 略 (lüè approximately).
Ā pà lā qì yà shānmài yǒu duō gāo?
How long is the Appalachian mountain range?
Dàyuē yī qiān wǔ bǎi yīnglǐ.
About 1500 miles.
大概 (dàgài) also means roughly, but it can also mean generally or probably.
Huǒchēzhàn jùlí zhèr duō yuǎn?
How far is the railway station from here?
Dàgài yào zǒu shífēn zhōng.
It’s about a ten minutes walk.
Tā dàgài bùhuì lái.
She is probably not coming.
Xiànzài jǐ diǎn zhōng?
What time is it now?
差不多 (chàbuduō) means nearly, almost or similar. Literally, 差不多 (chàbuduō) translates to “not much different”.
Xiànzài chàbuduō sān diǎn.
It’s almost three o’clock now.
Tāmen liǎng xiōngdì chàbuduō yīyàng gāo.
The two brothers are about the same height.
There are also words and phrases that give one a rough idea of the amount or the extent.
一点儿 (yīdiǎnr) means a little or a bit.
Qǐng nǐ gěi wǒ yīdiǎnr shuǐ.
Please give me a little water.
稍微 (shāowēi) and 有点儿 (yǒudiǎnr) mean a bit or a trifle. Often they are used together.
Wǒ shāowēi yǒudiǎnr lèi.
一眨眼的工夫 (yīzhǎyǎn de gōngfu) means in a blink.
喝一杯茶的工夫 (hè yī bēi chá de gōngfu) means the amount of time it takes to drink a cup of tea.
芝麻大小 (zhīmá dàxiǎo) means the size of a sesame seed.
拳头大小 (quántou dàxiǎo) means fist-size.
If you do know the quantities or measurements of the items, then you will need to specify the units for the value you provide. The various units of measure are discussed in Chapters 6 and 7 of “Learn Chinese through Songs and Rhymes“.