What Are Gas and Gwei?

What gas and gwei mean, how Ethereum fees are calculated after EIP-1559, and why every transaction needs gas to land in 2026.

Updated June 2026 · Reviewed by the PipeFlare team

Gas is the fee you pay to use Ethereum, and gwei is the tiny unit it's priced in

Every Ethereum and L2 transaction costs gas — paying too little fails, and failed transactions still cost real ETH

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About what is gas and gwei

Gas is the fee you pay to do anything on Ethereum. That includes sending ETH, swapping tokens, or using a smart contract. Gwei is the tiny unit that gas is priced in. One gwei equals one-billionth of an ETH. Gas exists because every action on Ethereum uses real computer power. Without a fee, anyone could spam the network for free. With gas, you bid for space in the next block.

How it actually works

Since the London upgrade on August 5, 2021, every gas fee has two parts. The first part is the base fee, set by the protocol each block. The base fee is burned, meaning the ETH is destroyed. The second part is the priority tip, which you pay the validator. Your total fee is (base fee + tip) multiplied by gas used. A simple ETH transfer uses 21,000 gas. A Uniswap swap can use 150,000 gas or more. The base fee moves up to 12.5% per block based on demand. Layer 2 networks bundle many transactions together and post the data back to Ethereum. That is why L2 fees are 10 to 100 times cheaper.

Start here

1Default to a Layer 2 like Base, Arbitrum, or Optimism so gas costs cents, not dollars.
2Check a live gas tracker like etherscan.io/gastracker before sending on mainnet.
3Lower the priority tip if your wallet pre-fills it — many wallets default too high.
4Double-check the transaction before signing — failed transactions still burn gas.

Strengths

Gas stops spam by making every action cost real money.
EIP-1559 makes fees easier to predict and burns the base fee, removing ETH from supply.
Layer 2 networks bring everyday gas costs down to a few cents or less.

Common misunderstandings

Mainnet gas can spike during busy times, making small sends too expensive to bother with.
Failed or reverted transactions still cost gas — a mistake is a real loss.
Bridging funds between L1 and L2 has its own one-time gas cost.

Common questions

What is gwei in simple terms?

Gwei is one-billionth of an ETH. It is the unit used to price Ethereum gas. Gwei keeps the numbers easy to read even when ETH costs thousands of dollars. A 20-gwei base fee on a 21,000-gas transfer comes to 420,000 gwei, or 0.00042 ETH.

Why does Ethereum need gas at all?

Every action on Ethereum uses real compute and storage. Without a per-action cost, someone could write an endless loop and freeze the network. Gas charges users in proportion to the work they ask the network to do. That keeps the network usable for everyone.

What is the base fee, and why is it burned?

After EIP-1559, the protocol sets a base fee each block based on demand. That fee is destroyed instead of paid to a validator. Burning removes ETH from circulation when the network is busy. During heavy use, more ETH can be burned than created, making Ethereum net deflationary. The priority tip you add still goes to the validator.

Why are Ethereum Layer 2 fees so much cheaper?

Layer 2 networks bundle many transactions and post compressed data back to Ethereum in blobs. The L1 cost gets split across hundreds of L2 users. After the Pectra upgrade on May 7, 2025, blob capacity doubled. L2 fees on Base, Arbitrum, and Optimism now routinely cost under one cent.

Do failed Ethereum transactions still cost gas?

Yes. A failed or reverted transaction still pays for the gas used up to the point of failure. A reverted Uniswap swap can cost real ETH even though no tokens moved. Always check the contract address, approvals, and slippage before signing.

Sources

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