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 格助詞（かくじょし） (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)’.
If we say it’s a car, this bike is something like a Lamborghini.
If we say Japan, is it something like bread? (Would this be considered bread in Japan)
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.
If said with Japanese, 'what's up' is equivalent to 'Genki'.
If we say it’s a computer, it is equivalent to Ram.
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’.