How a gas fee is built
Two numbers decide what you pay. The gas limit is how much computation the transaction needs. The gas price is what you pay per unit, quoted in gwei — a billionth of an ETH.
fee in USD = fee in ETH × ETH price
Since the fee market reform, the gas price splits into a base fee that is burned and a priority fee that goes to the validator. The base fee rises and falls automatically with how full recent blocks have been, which is why costs spike during heavy activity and settle within minutes of it ending.
Typical gas limits
| Action | Approximate gas limit |
|---|---|
| Send ETH | 21,000 |
| Send an ERC-20 token | 45,000–65,000 |
| Approve a token | 45,000 |
| Swap on a DEX | 120,000–200,000 |
| Mint an NFT | 150,000–250,000 |
| Bridge to a rollup | 90,000–150,000 |
Setting a higher limit than needed does not cost more — unused gas is refunded. Setting one too low does cost you, because the transaction fails and the gas consumed before it ran out is gone.
Paying less
- Time it. Base fees follow activity, and weekends and early UTC hours are consistently cheaper than the American afternoon.
- Batch approvals. Every token approval is its own transaction. Approving once for a sensible amount beats approving on every trade.
- Use a rollup. Layer 2 networks settle to Ethereum in batches, so a swap that costs several dollars on mainnet often costs a few cents.
- Do not overpay for priority. A large tip only helps when blocks are contested. In a quiet period it buys nothing.
When the fee is larger than the trade
On a $30 swap, a $12 fee is 40% of the position, and it is charged again on the way out. Small transactions on mainnet frequently cost more in gas than they can plausibly earn — which is worth checking against the trade itself in the profit calculator before signing.
Common questions
What is gwei?
A denomination of ETH equal to one billionth of one ETH. Gas prices are quoted in gwei because the amounts involved are far too small to express conveniently in whole ETH.
How do I calculate a gas fee?
Multiply the gas price in gwei by the gas limit, divide by one billion to get ETH, then multiply by the ETH price for the cost in dollars.
Why are gas fees so high sometimes?
The base fee rises automatically when blocks are full. Heavy activity such as a popular mint or a volatile market pushes it up, and it falls again once demand eases.
Do I get a refund if I set the gas limit too high?
Yes. You are only charged for the gas actually used. Setting a limit too low is the costly mistake, because the transaction fails and the gas spent is not returned.
How can I avoid high gas fees?
Transact during quieter hours, batch your approvals, and use a layer 2 network where the same operation typically costs a small fraction of mainnet.