# What is the relationship between Gwei and gas?

I know that a Gwei means 1000000000 wei, but when we send a transaction with 21000 gas, is that mean we send 21000 Gwei? please explain Gwei for me

Gas is needed by miners to execute a transaction. The more complicated a transaction is, the more gas they will need.

When you send a transaction, you can choose two things:

• The gas limit in `gas`: The maximum amount of gas the transaction is allowed to consume

• The gas price in `Gwei/gas`: How much Gwei you're willing to pay per unit of gas

Multiplying these numbers together, you get the maximum transaction fee you're willing to pay for the transaction in `Gwei`.

If you set the gas price to `1 Gwei/gas`, a transaction with a gas limit of `21000 gas` will cost you a maximum of `21000 Gwei`.

• So, is Gwei equal to gas? – zediziza Nov 4 '17 at 15:33
• @zediziza Only in transactions where the sender set the gas price equal to `1 Gwei/gas`. In transactions where the gas price is `15 Gwei/gas`, `1 gas` is equal to `15 Gwei`. – Jesbus Nov 4 '17 at 16:37
• So why we need create separate field instead of one. thanks. – hqt Mar 8 '18 at 19:38