# Transaction Fee

Gas refers to the transaction fee that will be charged to any transaction or execution on the Smart Contract in KardiaChain network. Gas is measured in HYDRO. 

1KAI = 10^18 HYDRO

1 OXY  = 10^9 HYDRO = 0.000000001 KAI

A transaction fee will be calculated by the following formula:

                      gasFee = gasPrice \* gasLimit

 The minimum gasPrice is 1 OXY (or 1000000000 HYDRO)

&#x20;The minimum gasLimit is 29000 and the maximum gasLimit is 20000000<br>

&#x20;A typical transaction gas limit for sending KAI on the network is 29000

&#x20;      1000000000 \* 29000 = 29000000000000 HYDRO = 0,000029 KAI

&#x20;A smart contract operation or any transaction on KardiaChain network will cost gas for computing the logic in KVM.

* It costs zero fee to read data from a smart contract.
* Gas will return to users if a smart contract execution does not spend all the gas fee.
* If the transaction is processed but not enough gas to pay, it will be dropped (failed) and gas won't be returned.


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