Sending the same amount of USDC can cost a fraction of a cent on one chain and several dollars on another. This article explains the reasons, and shows how to read the comparison chart on the live gas page.
If you are new to gas, read gas and fees explained first.
Block space is limited
Every blockchain produces blocks, and each block has a limited size. That limit is the block space. Users who want to be in a block compete for that space. If demand is higher than supply, the price goes up. If demand is low, the price falls.
This is the main reason for fee differences. A chain with a lot of free space and few users is cheap. A chain with a full block every time is expensive. Fees then also change over time: they rise in busy hours and drop when activity falls.
Chains tune supply in different ways. A chain can allow bigger blocks, make blocks more often, or run more work in parallel. Each choice has trade-offs for how easy it is to run a node and how decentralized the network stays.
Layer 1 and layer 2
A layer 1 (L1) is a base blockchain such as Ethereum or Bitcoin. A layer 2 (L2) is a separate chain that runs transactions on its own and then posts a record of them to a layer 1, to inherit its security. Arbitrum, Base and Optimism are L2s on Ethereum. See layer 1, layer 2 and layer 3 and rollups: optimistic and zero-knowledge.
An L2 can be cheaper because many users share the cost of one batch posted to Ethereum. Its own block space is also cheaper, as fewer people compete for it.
The two parts of an L2 fee
An L2 fee has two parts.
- L2 execution fee. The cost of running your transaction on the L2, priced like gas on Ethereum but usually far lower.
- L1 data fee. Your share of the cost of posting the transaction data to Ethereum so that anyone can check it.
On many L2s, the L1 data fee is the larger part. It depends on the size of the data and on what Ethereum costs at that moment. That is why a token transfer on an L2 can cost more when Ethereum itself is busy, even if the L2 is quiet.
The gas page adds the L1 data fee to the figure for Arbitrum, Base and Optimism, estimated for a typical transaction of each kind. So you compare total costs, not only the L2 part.
Blobs made L2s much cheaper
Before 2024, L2s posted their data to Ethereum as ordinary transaction data, which was expensive. EIP-4844 added a new kind of data space called blobs. Blobs are made for rollups. They are larger and cheaper than normal data and have their own fee market, separate from normal gas. Nodes keep them only for a limited time, which is enough for rollups to be checked.
The result is that the L1 data fee became much smaller for many L2 transactions. The exact amount changes with blob demand, so check the live numbers instead of relying on old figures.
Solana and Bitcoin work differently
Solana is a single fast layer 1 that processes many transactions in parallel. Its base fee is fixed per signature, so it stays tiny and stable. During busy times, users add a priority fee to jump the queue, mostly on popular programs. The details are in Solana priority fees.
Bitcoin has no gas and no smart contracts of the Ethereum kind. A Bitcoin fee is based on how big the transaction is in virtual bytes, not on the amount sent. Block space is scarce, so when many people want in, the price per byte goes up. See Bitcoin mempool and fees.
The price of the gas token matters
Each chain charges fees in its own coin: ETH on Ethereum, Arbitrum, Base and Optimism, POL on Polygon, SOL on Solana and BTC on Bitcoin. The fee in the coin is only half the story. To compare chains, you need the fee in dollars.
The same amount of gas can cost different dollars if the coin price is different. A fee of 0.0001 coin units means something different for a coin worth ten dollars than for a coin worth one thousand. This is why a tool that compares chains converts everything to US dollars using a current price. The price can be missing or late, so treat the dollar numbers as a good estimate.
Why a tip on a cheap chain can beat no tip on an expensive one
Speed options (economy, normal, fast) differ by tip. On an expensive chain, even the economy speed can cost more than the fast speed on a cheap chain. So a fast, tipped payment on the cheap chain can be cheaper than a slow, untipped one on the expensive chain.
The gas page shows this in its Compare chains chart. Each chain is a line with three points: economy on the left, normal in the middle and fast on the right. Height shows the cost in dollars, on a logarithmic scale, so each step up is a tenfold increase. A chain higher on the chart is more expensive.
How to read the chart
- Find the lowest line. The chain lowest at normal speed is the cheapest at that moment.
- A steep line means speed matters a lot on that chain: the fast price is far above the economy price.
- A flat line means speed barely changes the cost. On Arbitrum, all three speeds are the same, because tips are ignored there.
- Crossing lines show that the cheapest chain depends on the speed you pick. One chain can be cheapest at economy while another wins at fast.
- Use the buttons above the chart to switch between sending a coin, sending a token and a swap.
- Hover a line, or tap a chain name below the chart, to highlight it and see its three prices.
The amount you send does not change the fee on these chains. Sending 1 dollar and 1,000 dollars costs the same.
Frequently asked questions
Why are Ethereum fees higher than Layer 2 fees?
Ethereum mainnet has limited block space and many users compete for it. L2s run most of the work themselves, share the cost of posting data among many users, and use cheaper blob data space. Check the gas page for live numbers.
Why is Solana so cheap?
Its base fee is a small fixed amount per signature and the network can process many transactions in parallel. Busy programs can still add a priority fee, but it is often small.
Why does my L2 transaction cost more when Ethereum is busy?
Part of an L2 fee is the L1 data fee, which depends on Ethereum costs. When Ethereum gets more expensive, that part goes up, although L2 execution may stay cheap.
Is the cheapest chain always the best choice?
No. The receiver must be able to use the chain you choose, and the token must be the right version on that chain. Read the cheapest way to send USDC before you move money.
Why do fees change every few seconds?
Demand for block space changes constantly. Most chains update their price from recent blocks, so the live figure can move from one block to the next.