A gas limit is the maximum amount of gas, Ethereum's unit of computational work, that may be spent on a piece of activity. The term has two meanings. The transaction gas limit is set by the sender and caps how much work a single transaction may consume. The block gas limit is a network-wide ceiling on the total gas of all transactions packed into one block.
Both limits sit inside the fee model of the Ethereum blockchain and of the many Ethereum-compatible blockchains that copy it. The gas limit says how much work is allowed; the gas price says how much each unit of work costs. Multiplied together they give the most a sender can be charged, which is why wallets show both numbers before a user signs. The overall cost a user sees is described in the gas fee entry.
Gas limit in plain terms
Think of a taxi ride where you tell the driver, before setting off, the most you are willing to spend. If the trip costs less, you keep the change. If the meter reaches your limit before you arrive, the driver stops, and you still pay for the distance already covered.
The block gas limit is more like the size of a ferry. Every car (transaction) takes up some deck space. Once the deck is full, the remaining cars wait for the next sailing. A bigger ferry carries more cars per trip, but it is heavier to run, so the operators argue carefully before building a larger one.
The transaction gas limit
Every Ethereum transaction carries a gasLimit field. The Ethereum Virtual Machine (EVM) charges a fixed amount of gas for each operation it runs, and execution stops if the running total reaches the sender's limit. Three outcomes are possible:
- The transaction finishes under its limit. Only the gas actually used is charged, and the unused part is never taken from the sender's balance.
- The transaction runs out of gas. All of its state changes are reverted, but the gas consumed up to that point is still paid, because validators did the work of executing it.
- The limit is set too low for even the base cost. The transaction is rejected before it is included in a block.
A plain transfer of ether from one externally owned account (EOA) to another always costs 21,000 gas, so wallets set the limit at exactly that figure. Calls to a smart contract, such as a swap on Uniswap or a token transfer under the ERC-20 standard, use more and vary with the contract's logic. Wallets estimate the figure by simulating the call against the current state and usually add a safety margin, since the state can change before the transaction is mined.
The cost a sender authorises is bounded by:
- is the most gas the transaction may use.
- is the highest price per unit the sender accepts, usually quoted in gwei.
Example: a token swap with a gas limit of 150,000 and a maximum fee of 30 gwei can cost at most 150,000 × 30 = 4,500,000 gwei, which is 0.0045 ETH. If it actually uses 110,000 gas at an effective price of 12 gwei, the sender pays 1,320,000 gwei, or 0.00132 ETH.
The block gas limit
The block gas limit caps the total gas of every transaction in a block, which in turn caps how much computation and state growth the network absorbs per block. It is the main lever behind Ethereum's throughput, usually expressed as transactions per second (TPS), and plays the role that block size plays on Bitcoin.
Under the Ethereum Improvement Proposal (EIP) 1559 fee market, introduced in the London upgrade of August 2021, each block has a target of half the limit. When blocks are fuller than the target, the base fee rises; when they are emptier, it falls. In the months before London the limit stood at about 15 million gas; London kept 15 million as the target and set 30 million as the maximum.
The limit is not fixed in the protocol rules. Each block proposer may move it by a small fraction (1/1024) of the parent block's limit, in the direction set in its client software, so the figure drifts toward whatever most proof-of-stake validators signal. No hard fork is needed. Validators used this mechanism in 2025 to raise the limit from 30 million to 36 million gas (February), then to 45 million (July), and to 60 million in late November 2025. The Fusaka upgrade of 3 December 2025 made 60 million the client default (EIP-7935).
Per-transaction cap since Fusaka
Until December 2025 a single transaction could, in principle, consume an entire block. Fusaka added EIP-7825, which caps any one transaction at 16,777,216 gas, which is . The cap separates the two limits: blocks can keep growing while the largest single job stays bounded, which makes future parallel execution easier and limits denial-of-service risk. Transactions requesting more than the cap are rejected.
Trade-offs and debate
Raising the block gas limit increases capacity and tends to lower fees, but it also makes blocks larger and slower to verify, raises storage needs for each full node, and can push out home operators with modest hardware. Ethereum's developers have therefore favoured gradual increases, alongside moving activity to Layer 2 networks such as optimistic rollups and ZK-rollups, which post compressed data back to the main chain. Proposals such as EIP-4488 were part of that effort to make rollup data cheaper.
For users, the practical points are simpler. A limit set too low wastes the fee on a failed transaction; a limit set generously costs nothing extra, since unused gas is not charged. Large limits on unfamiliar contracts can be a warning sign when a crypto wallet cannot simulate what the call will do.