What are gas fees? In plain words
Someone pays you 40 USDC on Base. You can see it in your wallet app, plain as day. You try to send 10 of it to a friend, and the app says you do not have enough funds.
It sounds like a bug, and it trips up a lot of newcomers. You have plenty of USDC, which is a digital dollar. What you do not have is the thing that pays for the send.
Every envelope needs a stamp
A blockchain, or chain for short, is a shared record of who owns what. Any action that changes that record is called a transaction: a payment, a trade, a permission you give an app. Each one costs a small fee, called gas. Gas pays for the work of running the chain, which means the computers that check and record what you asked for.
Think of postage. Each transaction is an envelope, and it needs a stamp before it can go. Three things follow from that:
- The sender buys the stamp. Receiving tokens costs you nothing.
- Looking at your balance is not an envelope, so it needs no stamp.
- A heavier item costs more to post. A trade takes more work than a simple send, so it usually needs more gas.
The stamp comes in the local coin
Here is the part that catches people out. The stamp has to be bought in the chain’s own coin, not in the token you are sending.
- On Ethereum, Arbitrum, Base and Optimism, that coin is ETH.
- On BNB Chain, it is BNB.
- On Polygon, it is POL.
So back to the 40 USDC on Base. To send it, you need two things in the same place: the USDC, and a little ETH on Base. ETH on Arbitrum will not do, because that ETH lives on a different chain. Once enough ETH reaches your wallet on Base to cover the gas, the same send can go through.
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A few apps can arrange gas for you, which is why this is usually true and not true every time. As a starting point, though, expect to need the local coin.
Why the price of a stamp moves
Gas is not a fixed price. Each chain has limited room, so when it is busy, people pay more to get in. When it is quiet, it costs less. The same send can cost more at one hour than at another. Your wallet shows an estimate before you sign, the step where you agree to the transaction, so you can look before you go ahead.
A transaction can also fail. A trade might stop because the price moved, for example. Your tokens stay where they were, but the gas is still spent, because the computers did the work. It is like postage on a letter that comes back.
What people get wrong
“The fee comes out of my USDC.” Usually it does not. If you send 10 USDC, your friend gets 10 USDC, and the gas comes out of your ETH.
“I can send all of my ETH.” Sending ETH needs gas too. Empty a chain’s coin down to zero, and any other tokens you hold there can get stuck until you add more.
“One coin covers every chain.” Each chain needs its own coin, on that chain.
So the habit is simple: before you send, check that you have enough of the local coin on that chain to cover the fee. That clears the problem that stalled the send at the top, though having gas does not mean every transaction succeeds.
In short
- Every transaction pays a small fee called gas, for the work of running the chain.
- Gas is paid in the chain’s own coin: ETH, BNB or POL, depending on the chain.
- Gas costs more when the chain is busy, and a failed transaction still spends it.
- To send USDC on Base, you usually also need a little ETH on Base.
More one-minute DeFi explainers: cleave.fi/blog
