The five gas variables, in plain English

Every Ethereum transaction fee is the product of five numbers. The calculator above handles the math; this section explains what each one means so you can interpret what your wallet shows.

Gwei (per-unit gas price)

A denomination of ETH. 1 gwei = 10⁻⁹ ETH = 0.000000001 ETH. Gas prices are quoted in gwei because the raw ETH numbers would be awkward fractions. When someone says “gas is 30 gwei,” they mean the network is charging 30 × 10⁻⁹ ETH per gas unit.

Gas units (transaction complexity)

The amount of computational work your transaction does. ETH transfer = 21,000 units (protocol minimum). ERC-20 transfer ≈ 55,000. Uniswap swap ≈ 150,000. The more the contract does, the more gas units it consumes. This number is determined by the code being called, not by you.

Base fee (the floor)

Set automatically each block by the protocol (EIP-1559). Goes up when the previous block was >50% full, down when it was <50%. This component gets burned — removed from circulation. It's the minimum gas price for inclusion.

Priority fee / tip (your speed bid)

The optional tip you add on top of base fee to incentivize validators to include you ahead of other transactions. Wallet's “rapid” tier is just a higher tip. Tips go to the validator who proposed the block — not burned.

ETH/USD price (the conversion)

You pay the fee in ETH. The USD figure is just for human comprehension. When ETH moves 5%, every gas fee on every page on this site moves with it — without any change in gwei.

The fee formula: fee_eth = gas_used × (base_fee + priority_fee) × 10⁻⁹ then multiply by the live ETH/USD price.

Why your wallet's quote doesn't match this calculator

The math here is exact: gwei × gas-units × ETH price = USD fee. But when MetaMask or Rabby shows you a transaction confirmation, the number is often 15-40% higher than what you'd expect from this page. Five reasons, in descending order of impact:

• Gas-limit padding (10-30%). Wallets quote the max possible fee, not the expected fee. The actual gas used is usually less than the limit; the excess is refunded.
• Aggressive priority fee. MetaMask's default is the “market” tier, which adds a 1-2 gwei tip on top of base fee for faster inclusion. The calculator here defaults to base-fee only unless you specify otherwise.
• Live-vs-quote drift. The wallet's gwei quote freezes when you open the confirmation modal. If you stare at it for 20 seconds, the actual base fee may have shifted up or down. The number on this page refreshes every 60 seconds.
• L2 wallet fees include L1 data. If you're sending on Arbitrum, Optimism, or Base, the wallet folds in the L1 data-posting fee. This calculator is mainnet-only — for L2 cost, see the L2 gas fees page.
• Permit2 or approval bundling. Some dApps inline an approval into the same transaction as the swap. The wallet shows one fee, but it covers two operations.

To see what you actually paid for a transaction, check the Etherscan receipt after it confirms — the “Transaction Fee” field there is real cost, gas_used × gas_price. That's the number this calculator matches, not the wallet's pre-confirmation estimate.