# what is difference between "gas" "gas price" and "fee"?

Can we say that `gas` is the unit of transaction fee ?

And `gas price` is the same transaction fee ?

If so, why we do not use `ether` and `wei` instead of `gas` ?

• Jul 18, 2018 at 12:48

## 1 Answer

in a nutshell :

gas is the cost unit

gas price is a single gas unit's price

and

Fee= gas*gas price

why using gas instead wei?

because we need a fixed value (unit) for expressing the operations cost. then this initial cost is "translated" in wei/ether which may vary according to the market.

"y operation"= x gas => x gas * market gas price= your fee (Z).

so "y operation" cost will be always x gas, today as in next year, but z will change as the gas price will change.

• Thank you for your complete and clear answer. However, in my opinion it is still possible to use `ether` and `market ether price` instead of `gas` and `market gas price`. ex. `tx fee = n gas` when `gas price = m` is equivalent of `tx fee = a ether` when `ether price = b USD`. maybe I do not consider somethings .... Jul 18, 2018 at 12:27
• The Vm doesn't know whether the ether price goes up or down. it knows only that a given operation costs a given amount of a fictive unit gas and it let us decide in the market what this unit price according to ether fluctuation. Jul 18, 2018 at 12:28