Ethereum Gas Fees Explained: Base Fee, Priority Fee and Gas Limit

Ethereum gas fees explained: how the base fee, priority fee and gas limit combine into what you pay, with worked numbers and a checklist before you send.

What is gas on Ethereum?

Every action on Ethereum uses computation, and the network measures that work in units called gas. A plain ETH transfer uses 21,000 gas. Moving a token, approving a contract or swapping on a decentralized exchange uses more, because the network has to run contract code.

You pay for gas in ETH, but the price is quoted in gwei, a unit equal to one billionth of an ETH. So every fee has two independent parts: how many gas units your transaction uses, which depends on what it does, and the price per unit, which depends on how busy the network is when your transaction lands. If the unit is new to you, start with what gwei is and how to convert it.

The fee formula in one line

Under the fee market defined in EIP-1559, the price per gas has two pieces: a base fee set by the protocol and a priority fee, or tip, that you choose. Multiply their sum by the gas your transaction actually uses and you have the fee.

Here is the figure’s example in full. Suppose a token swap uses 150,000 gas while the base fee is 24 gwei and your tip is 1.5 gwei. The fee is 150,000 × 25.5 = 3,825,000 gwei, which is 0.003825 ETH. At a hypothetical ETH price of $3,200, that is $12.24.

The two pieces go to different places. The base-fee portion, 150,000 × 24 = 3,600,000 gwei (0.0036 ETH, or $11.52), is burned, meaning it is removed from circulation. Only the tip portion, 150,000 × 1.5 = 225,000 gwei (0.000225 ETH, or $0.72), goes to the validator who includes your transaction.

What is the base fee, and why does it change?

The base fee is the minimum price per gas that every transaction in a block must pay, and you cannot negotiate it. The protocol calculates it from the previous block. Each block has a gas target equal to half the block gas limit: when the previous block used more than the target, the base fee rises, and when it used less, the base fee falls.

The adjustment is capped at 12.5% per block. A completely full block, twice the target, raises the next base fee by exactly 12.5%, and an empty block lowers it by 12.5%. As of September 2026, the block gas limit is roughly 60 million gas, so the target is about 30 million; an upgrade expected in the second half of 2026 aims to raise capacity further.

The cap makes the base fee predictable over a few blocks but not over many, because the changes compound. Starting from a hypothetical 8 gwei:

Ten full blocks in a row multiply the base fee by about 3.25. That is how fees can jump quickly during a popular launch or a sharp market move, and why they usually drift back down once demand fades.

What is the priority fee (tip)?

The priority fee is an extra amount per gas paid to the validator who proposes the block. It is the part of the price you control, and it matters most when blocks are full and transactions compete for space. When blocks are running below target, a small tip is usually enough to be included within a few blocks.

In a modern (type 2) transaction you set two prices: a max priority fee, which is the tip you offer, and a max fee, which is the most you will pay per gas with the tip included. The tip actually paid is the smaller of your max priority fee and your max fee minus the base fee. With a max fee of 20 gwei, a max priority fee of 2 gwei and a base fee of 19 gwei, the validator receives only 1 gwei of tip, and your total price is 20 gwei per gas.

What is the gas limit?

The gas limit is the maximum number of gas units you allow a transaction to use. It is a ceiling on quantity, not a price. A simple ETH transfer to an ordinary address needs exactly 21,000 gas; for contract interactions, your wallet estimates the amount by simulating the transaction and usually adds a margin. Typical figures for everyday actions are collected in our gas estimates for transfers, swaps and approvals.

You are charged only for the gas actually used, so a generous limit costs nothing extra when things go well. The risk runs the other way: if a transaction hits its limit before finishing, it fails, its changes are reversed, and the gas it consumed is still charged. That is the most common answer to why a failed transaction still costs gas.

Warning: Lowering the gas limit below your wallet’s estimate rarely saves money. If the transaction needs more gas than you allowed, you pay for a failure and then pay again to retry.

Two other limits exist at the protocol level. The block gas limit caps the total gas in each block, and since the Fusaka upgrade in December 2025 a single transaction is also capped at about 16.78 million gas. Everyday transfers and swaps come nowhere near either cap.

Max fee: your protection against spikes

The max fee per gas is your ceiling on price. Your transaction pays the base fee at the moment it is included plus the effective tip, and anything between that and your max fee is never charged. Before inclusion, the protocol also requires your balance to cover the worst case, gas limit × max fee, and your wallet checks the amount you are sending on top of that.

A common rule of thumb, and the default in our gas fee calculator, sets the max fee at twice the current base fee plus the tip. Because each full block can raise the base fee by at most 12.5%, that buffer survives five full blocks in a row (1.125^5 ≈ 1.80 times the starting base fee) but not six (about 2.03 times).

Worked example: reserved vs charged

Continuing the swap above, suppose your wallet sets these values:

You need $28.51 worth of ETH available for the transaction to be valid, but you pay $12.24. If the base fee climbs above 49.5 gwei before your transaction is included, it waits instead of paying more. From there you can keep waiting or replace it with a higher fee, as explained in how speed-ups and replace-by-fee work.

Why does my wallet say I don’t have enough ETH for gas?

Because the worst case is reserved up front. Suppose you hold 0.2 ETH and want to empty the wallet with a plain transfer while the base fee is 15 gwei and your tip is 1 gwei. With a max fee of 2 × 15 + 1 = 31 gwei, the worst case is 21,000 × 31 = 651,000 gwei, or 0.000651 ETH, so the most you can send is 0.199349 ETH.

If the base fee stays at 15 gwei, the actual fee is 21,000 × 16 = 336,000 gwei (0.000336 ETH), leaving 0.000315 ETH behind. Tokens are the other trap: moving a token on Ethereum costs gas paid in ETH, so a wallet that holds only tokens cannot send them until it also holds a little ETH.

How much does the same transaction cost on a quiet vs busy network?

Gas units are fairly stable for a given action; the price per gas is what swings. The table compares a quiet hypothetical network (0.5 gwei base fee plus 0.05 gwei tip) with a busy one (40 gwei base fee plus 2 gwei tip), with ETH at a hypothetical $3,200.

Every row in the busy column is about 76 times the quiet one. In spring 2026, ethereum.org reported typical gas prices below 1 gwei, but that is a snapshot rather than a promise, and demand can change within minutes.

Size matters too. On the busy network, a $50 token transfer would cost $8.74, or 17.47% of the amount; the same fee on $2,000 is 0.44%. Layer 2 networks exist largely to shrink this cost, and why rollups are cheaper explains how they do it.

How to check live gas prices before you send

Step 1: Read your wallet’s fee screen

Open the advanced or custom fee view. You should see the estimated base fee, your max fee, your max priority fee and the gas limit. If your wallet shows only a dollar figure, remember that it is an estimate built from those four numbers.

Step 2: Cross-check on a block explorer

A block explorer such as Etherscan shows the latest base fee and suggested tips. Compare it with your wallet’s estimate; a large mismatch is a reason to pause.

Step 3: Convert to dollars yourself

Multiply the gas estimate by base fee plus tip, divide by one billion to get ETH, and multiply by the current ETH price. The calculator below does the same arithmetic and also shows the worst case at your max fee.

Common mistakes that waste gas

• Cutting the gas limit to save money. You pay only for gas used, so a lower limit adds failure risk and nothing else.
• Paying a high tip on a quiet network. When blocks are below target, a larger tip rarely buys faster inclusion.
• Setting a tight max fee during volatile periods. The transaction can sit pending while the base fee climbs.
• Ignoring the fee as a share of the amount. A fixed gas cost hurts small transactions most.
• Approving unlimited token allowances by habit. Each approval is a separate paid transaction and a lasting permission; see why to review and revoke token approvals.
• Treating gas as the only cost. Swaps also carry price impact and slippage, and exchanges charge their own withdrawal fees on top of network fees.

A decision rule for timing a transaction

Before sending, compute the fee as a percentage of what you are moving. If it is above a threshold you set in advance, for example 1%, and the transaction is not urgent, you have three levers: wait for a lower base fee, combine several actions into fewer transactions, or use a layer 2 network. If it is urgent, raise the tip rather than cutting the gas limit.

The same logic works on other chains, even though Bitcoin prices block space per virtual byte rather than per unit of gas; see how Bitcoin fees are calculated in sat/vB. For a full cost picture that includes maker, taker and spread costs on exchanges, use a fair way to compare crypto fees.

The bottom line

An Ethereum fee is gas used × (base fee + tip). The protocol sets and burns the base fee, you choose the tip, the gas limit caps quantity and the max fee caps price. Check live values right before sending, judge the fee against the amount, and never lower the gas limit to save money.

This content is for education only and is not financial, investment, tax or legal advice. Crypto assets are volatile and you can lose money. Examples use hypothetical numbers. See our disclaimer and editorial policy.