で言(い)うとIn, Of, According to

でいうと is an expression in Japanese that is commonly used to ask questions, or to give information about how one thing corresponds with another. It is a combination of the case marking particle で meaning 'with', and 言(い)うと meaning 'if said', or 'if we say'.

This structure will be seen after nouns, and can be translated as 'if said with (A), (B)'.

• このバイクは、車(くるま)で言(い)うとランボルギーニみたいなものだ。

  If we say it's a car, this bike is something like a Lamborghini.
• 日本(にほん)で言(い)うとパンみたいなもの？

  If we say Japan, is it something like bread? (Would this be considered bread in Japan)
• 一言(ひとこと)で言(い)うと彼(かれ)は本当(ほんとう)に凄(すご)い人(ひと)だ。

  If said in a word, he is an amazing person.

でいうと will often be seen in sentences with に当(あ)たる 'to be equivalent to', another common grammar structure used for drawing connections between things.

• 「What's up」は日本語(にほんご)でいうと、「元気(げんき)」に当(あ)たる。

  If said with Japanese, 'what's up' is equivalent to 'Genki'.
• コンピューターでいうとＲＡＭ(アールエーエム)に当(あ)たる。

  If speaking about computers, it is equivalent to RAM.

Fun Fact

一言(ひとこと)で言(い)うと is a set expression that means 'to put it in a word', 'in short', or 'to sum up'.

• 一言(ひとこと)で言(い)うと彼(かれ)とはもう会(あ)わないことにした。

  To sum it up, I have decided to never see him again.