Deciphr Academy
Track 1 · Foundations · Module 5

Transactions, gas and fees

What you pay, why it changes, and why failed transactions still cost money.

Lessons
6
Reading
37 min
Quiz
15 questions
Pass mark
80%
  1. 1What a transaction containsWhat is inside an Ethereum transaction?5 min
  2. 2Gas explainedWhat is gas in Ethereum?6 min
  3. 3Base fee and tipWhat are the base fee and the priority fee on Ethereum?7 min
  4. 4Nonces and stuck transactionsWhat is a nonce, and why do Ethereum transactions get stuck?7 min
  5. 5Failed transactions still cost gasWhy do failed Ethereum transactions still cost gas?6 min
  6. 6Paying less in feesHow can you pay lower gas fees on Ethereum?6 min

The case used in this module

Each module tells its own made-up Brindlecove story, so details can differ from one module to the next.

Key words

Transaction
A signed instruction from an account, such as sending ETH to an address.1
Gas
The unit that measures how much computing work an action on Ethereum needs.2
Gwei
A tiny unit of ETH. 1 ETH is 1,000,000,000 gwei.23
Wei
The smallest unit of ETH. 1 gwei is 1,000,000,000 wei.2
Gas limit
The most gas a transaction is allowed to use.21
Base fee
The lowest price per unit of gas a block accepts. The network sets it, and it is burned.24
Priority fee (tip)
An extra price per unit of gas, paid to the validator who includes your transaction.23
Max fee
The most you will pay per unit of gas, base fee and tip included.1
Nonce
A counter that numbers each transaction from an address, starting at 0.51
Burn
Destroying ETH so that nobody receives it. The base fee is burned.42
Revert
When a contract stops and undoes its changes. The gas used so far is still paid.62
Layer 2
A network built on top of Ethereum that offers lower fees.3
Sources
  1. Transactions. ethereum.org developer docs, page updated 7 October 2026.
  2. Gas and fees. ethereum.org developer docs, page updated 24 June 2026.
  3. Gas fees. ethereum.org, page updated 8 April 2025.
  4. EIP-1559: Fee market change for ETH 1.0 chain. Ethereum Improvement Proposals (Vitalik Buterin and others), created 13 April 2019, status Final.
  5. How To "Cancel" Ethereum Pending Transactions?. Etherscan Information Center, 23 July 2020, updated 21 June 2026.
  6. EIP-140: REVERT instruction. Ethereum Improvement Proposals (Alex Beregszaszi, Nikolai Mushegian), created 6 February 2017, status Final.