Quick answer
Gas fees are payments made to Ethereum validators (computers that process transactions) to compensate them for the computational work of including your transaction in the blockchain. Fees are measured in gwei (a tiny fraction of ETH) and fluctuate based on network demand. During busy periods, fees can be £20-100 per transaction. Using Layer 2 networks like Arbitrum or Base reduces fees to under £0.10.
What are gas fees and why do they exist?
Every operation on Ethereum — sending ETH, swapping tokens, depositing in a lending protocol — requires computational work from the computers (validators) that maintain the network. Gas fees are how that work is compensated.
The term 'gas' is a deliberate metaphor from the early Ethereum design: just as a car needs petrol (gas) to run, Ethereum operations need gas to execute. Different operations consume different amounts of gas based on their computational complexity. A simple ETH transfer uses 21,000 gas units. A complex DeFi transaction might use 300,000 or more gas units.
Gas fees have two purposes: compensating validators for processing transactions, and preventing spam. Without a cost for transactions, someone could flood the Ethereum network with millions of useless transactions and grind it to a halt. Gas fees make this prohibitively expensive.
How is the gas fee actually calculated?
Since Ethereum's EIP-1559 upgrade in August 2021, gas fees have two components:
- Base fee
- Set automatically by the Ethereum protocol based on how full the previous block was. If the network is congested, the base fee rises. If it is quiet, it falls. The base fee is burned (destroyed) rather than paid to validators. This makes ETH deflationary when the network is busy.
- Priority fee (tip)
- An optional extra payment you offer validators to incentivise them to include your transaction faster. During periods of high demand, you may need a meaningful tip to avoid long waits. During quiet periods, a minimal tip (1 gwei) is usually sufficient.
- Max fee
- The maximum total fee you are willing to pay per unit of gas. You will never pay more than this, and you receive a refund if the actual cost is lower. Setting this too low means your transaction may wait or not be included at all.
- Gwei
- The unit in which gas is measured. 1 gwei = 0.000000001 ETH (10^-9 ETH). When people say 'gas is 15 gwei', they mean each unit of gas costs 15 gwei. Multiply gas units used × gas price in gwei to get the total fee in gwei, then convert to ETH and then to your local currency.
Why do gas fees change so dramatically?
Ethereum can process approximately 15 transactions per second on mainnet. When demand exceeds this capacity, transactions queue up and users compete by offering higher fees to get included faster. This creates a dynamic fee market that can swing from 5 gwei (cheap) to 500 gwei (extremely expensive) in hours.
Major events that cause gas fee spikes include: popular NFT mints (thousands of people trying to buy simultaneously), market crashes or surges (everyone trying to trade at once), major protocol launches attracting immediate attention, and large liquidation events triggering cascading automated trades.
| Gas price (gwei) | Approx. ETH transfer fee | Approx. Uniswap swap fee | Condition |
|---|---|---|---|
| 5-10 | £0.30-0.60 | £1-3 | Network very quiet |
| 20-30 | £1.20-1.80 | £5-10 | Normal weekday |
| 50-100 | £3-6 | £15-40 | Busy period |
| 200-500 | £12-30 | £60-180 | Peak congestion (NFT launch etc.) |
Gas fees are almost always lowest at weekends (especially Sunday evening UTC), during Asian nighttime hours, and between 00:00-08:00 UTC on weekdays. Checking a gas tracker before transacting can save you significant money.
How to check current gas prices before transacting
- 01
Etherscan Gas Tracker
Visit etherscan.io/gastracker — shows current gas prices in gwei for slow, average, and fast transaction speeds, with estimated wait times and the current base fee. The most reliable real-time source.
- 02
MetaMask built-in estimate
When MetaMask shows you a transaction confirmation, it displays the estimated gas fee in ETH and your local currency. Click 'Edit' to choose between low, market, and aggressive speed options. You can also manually set a custom max fee.
- 03
Gas price alerts
Apps and browser extensions (like Gas Price Now) can alert you when gas drops below a threshold you set. Useful if you have a non-urgent transaction and want to wait for a cheaper moment.
- 04
Time your transactions
If your transaction is not time-sensitive, delay it until a low-traffic period. Weekend evenings and early morning UTC are typically cheapest.
Layer 2 networks: the practical solution to high gas fees
Layer 2 (L2) networks are built on top of Ethereum and inherit its security but can process transactions far more cheaply by batching many transactions together and submitting them to Ethereum as a single compressed record. The same DeFi protocols (Uniswap, Aave, Curve) run on Layer 2 networks with identical functionality but at 10-100x lower fees.
- 01
Bridge ETH to Arbitrum
Visit bridge.arbitrum.io, connect MetaMask (set to Ethereum Mainnet), enter how much ETH to bridge, confirm. You pay one Ethereum mainnet gas fee for the bridge transaction. ETH arrives on Arbitrum in 5-15 minutes.
- 02
Switch MetaMask to Arbitrum
In MetaMask, click the network dropdown, select Arbitrum One. Your bridged ETH now shows in your MetaMask balance on Arbitrum.
- 03
Use DeFi normally on Arbitrum
Navigate to any protocol that supports Arbitrum — Uniswap, Aave, Curve all do. Connect your wallet on the Arbitrum network and transact normally, paying only Arbitrum's minimal gas fees.
| Network | Typical swap fee | Time to confirm | Notes |
|---|---|---|---|
| Ethereum Mainnet | £5-50 | 15-60 seconds | Highest security, highest fees |
| Arbitrum One | £0.01-0.50 | 1-3 seconds | Most DeFi liquidity, very mature |
| Base | £0.01-0.20 | 1-2 seconds | Coinbase's L2, growing fast |
| Optimism | £0.01-0.30 | 1-2 seconds | OP Superchain ecosystem |
| Polygon | £0.001-0.10 | 2-5 seconds | Different security model (sidechain) |
What happens if I set gas too low?
If you set your max fee below the network's base fee, your transaction will not be included in any block — it remains in the mempool (pending pool) indefinitely. Most wallets will eventually drop it automatically after a period of time.
If you set gas that used to be acceptable but the network congestion increases before your transaction is picked up, it may stay pending. You can cancel or speed up a pending transaction by submitting a new transaction with the same nonce (sequence number) and a higher gas fee.
Frequently asked questions
Does MetaMask charge gas fees?
MetaMask does not charge gas fees — gas fees go to Ethereum validators. MetaMask displays and manages your gas settings but takes no cut. MetaMask earns revenue separately through its token swap feature, which includes a small markup when you use MetaMask's built-in swap rather than going to a DEX directly.
Why do I need ETH to pay gas when I am sending USDC?
Gas is always paid in ETH on Ethereum and Ethereum Layer 2 networks, regardless of which token you are moving. Even if you are sending USDC stablecoins, you need some ETH in your wallet to pay the network fee. This is a common stumbling block for new users — always keep a small ETH balance for gas.
What is EIP-1559 and how did it change gas fees?
EIP-1559 is an Ethereum upgrade from August 2021 that reformed the gas fee market. Before it, users bid in a blind auction for block space, leading to massive fee overpayment. EIP-1559 introduced a protocol-set base fee that adjusts block by block based on demand, plus an optional tip for validators. It also burns the base fee, removing ETH from circulation. This made fees more predictable and made ETH slightly deflationary during high-usage periods.
Can I get a refund on a failed transaction?
Your principal is returned if a transaction reverts (fails). However, the gas fee is not refunded — the network still used computational resources to process and fail the transaction. This is why it is important to review transactions carefully before confirming.
What is the cheapest blockchain to transact on?
Solana and Tron are among the cheapest for simple transfers, often under £0.001. Ethereum Layer 2 networks (Arbitrum, Base) offer very low fees (£0.01-0.50) while inheriting Ethereum's security. Ethereum mainnet is among the most expensive for complex operations. The 'cheapest' network depends on what you are doing — for DeFi specifically, Arbitrum or Base offer the best balance of low fees and deep liquidity.