L2 bridge fee calculator
Canonical vs third-party bridges. Know the spread before you bridge.
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Bridging ETH from mainnet to Arbitrum, Optimism, or Base runs $2-15 depending on gas conditions and bridge choice. Canonical (official) bridges are cheapest one-way but slow coming back (7-day withdrawal for Optimistic rollups). Third-party bridges (Across, Hop, Stargate) charge 0.05-0.25% but offer 5-minute round-trips.
This calculator estimates the fee you'll pay for a given bridge amount and route. Use it to decide if the L2 is worth bridging to for your specific use case.
The economics of L2 bridging shifted materially in March 2024 when Ethereum's Dencun upgrade (EIP-4844) went live. Before Dencun, L2s posted compressed transaction data to Ethereum mainnet as calldata, costing $0.25-$2.00 per L2 transaction for the data-posting overhead. After Dencun, L2s post data as 'blobs' — a cheaper storage format that costs roughly 10x less. Average Arbitrum transaction fees dropped from $0.40 to $0.04 overnight. Base fees dropped from $0.20 to $0.02.
For any transaction under $5,000, bridging and transacting on an L2 now almost always beats mainnet by a factor of 100x or more on gas. The relevant question is no longer 'should I use L2' but 'which L2 for this specific use case' — Arbitrum for deepest DeFi liquidity, Base for Coinbase ecosystem and consumer apps, Optimism for Superchain infrastructure, zkSync or Starknet for zk-proof security with faster finality.
Bridge $2,000 of ETH from mainnet to Base
Canonical Base bridge: ~$1.50 gas (L1 + L2).
Across Protocol (third-party): 0.04% fee = $0.80, plus ~$0.50 gas = $1.30.
Stargate: 0.06% fee = $1.20 + gas = ~$2.50.
On Base, 50 subsequent swaps cost ~$0.05 each = $2.50. Total pays for itself in one decent trading session.
When to use canonical vs third-party bridges
Canonical (L2 → L1 withdrawal): Arbitrum is ~7 days, Optimism/Base are ~7 days (Optimistic rollup challenge period). zkSync/Starknet/Polygon zkEVM are faster (minutes to hours). For return bridging in a hurry, use third-party bridges like Across or Stargate — they front the liquidity and charge 0.05-0.25% for the privilege.
Bridge security considerations
Canonical bridges are secured by the L2's trust assumptions (usually as safe as the L2 itself). Third-party bridges are separate smart contract systems — Wormhole was hacked for $325M in 2022; Nomad lost $190M that same year; Multichain collapsed with $125M stuck in 2023. Stick to battle-tested bridges (Across, Hop, Stargate, canonical) for any >$5K.
L2 fee breakdown: what you're actually paying for
An L2 transaction fee has two components. The L2 execution fee is what the L2 sequencer charges for processing your transaction — this is $0.01-$0.10 for most simple swaps post-Dencun. The L1 data fee is the amortized cost of posting your transaction batch to Ethereum mainnet. Post-EIP-4844, this L1 component dropped from ~70% of total fee to ~10%, dramatically reducing total cost.
Sequencer revenue is how L2 companies monetize. Arbitrum, Base, and Optimism collect the difference between gas fees charged and actual costs. Base generated over $10M in sequencer revenue in Q4 2024 alone — that revenue goes to Coinbase, the L2 operator. Users pay these fees indirectly. This is why L2 operators have a strong incentive to keep fees just low enough to attract users, not as low as technically possible.
Cross-chain liquidity fragmentation: the real cost of L2 proliferation
With 50+ active L2 and sidechain networks, liquidity is fragmented. A $50,000 USDC position on Arbitrum is separate from USDC on Base, Optimism, zkSync, and mainnet. Market makers and DeFi protocols quote different rates on each chain, meaning the same trade can cost 5-15 bps more on a thin L2 versus deep Arbitrum or mainnet liquidity.
Intent-based bridging (Across Protocol's model) partly solves this by using a network of liquidity providers ('relayers') who fill orders across chains instantly and settle later. The user experience is fast and cheap; the LP takes bridge-risk in exchange for the fee. For amounts under $100K, intent-based bridges like Across are typically the best combination of speed, cost, and safety. Above $100K, canonical bridge + 7-day wait is often worth it to avoid bridge LP slippage and smart contract risk.
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L2 bridging — frequently asked questions
Why does the canonical bridge take 7 days from L2 to L1?
Optimistic rollups (Arbitrum, Optimism, Base) assume transactions are valid unless challenged within a 7-day window. Withdrawing before the window closes would let a malicious proposer steal funds. This is a trust assumption built into the rollup design. zk-rollups (Starknet, zkSync) don't have this because validity is proven cryptographically — withdrawals can be hours instead of days.
Is there a cheaper bridge than the canonical?
For L1 → L2 deposits, canonical is almost always the cheapest because the L2's fraud-proof system subsidizes the verification. For L2 → L1, third-party bridges beat canonical on speed (5 min vs 7 days) and sometimes on cost when gas is low. Across, Hop, and Stargate are the most liquid options.
Can I bridge between two L2s directly (Arbitrum to Base)?
Yes, via third-party bridges. Direct L2-to-L2 saves time vs the canonical round-trip (L2 → L1 → L2). Across, Stargate, and Orbiter support most L2-to-L2 routes with 0.05-0.2% fees. Be aware of bridge security risks for any route.
Are L2 tokens and L1 tokens the same asset?
Bridged tokens on L2 are typically wrapped representations of the L1 asset. ETH on Base is native (same as L1 ETH). USDC on Base is 'Base USDC' — different token contract but 1:1 redeemable with canonical USDC. Some L2 tokens (Arbitrum's ARB, Optimism's OP) are their own assets with their own supply and governance.
What's the best L2 for low-gas transactions?
Base and Arbitrum are consistently cheapest ($0.02-$0.10 per swap under normal conditions). Optimism and zkSync are similar. Polygon PoS (not a true rollup) is historically cheapest ($0.01) but has different security trade-offs. For DeFi, Arbitrum has the deepest liquidity; for consumer apps, Base has the strongest ecosystem post-Coinbase backing.
How much did EIP-4844 (Dencun) actually reduce L2 fees?
Dramatically. Arbitrum average transaction fees dropped from ~$0.40 to ~$0.04 — a 90% reduction — the day Dencun activated in March 2024. Base fees dropped from ~$0.20 to under $0.02. Optimism dropped similarly. The blob data storage format is 10-100x cheaper than calldata for equivalent data volume, and L2s immediately started using blobs. Users saw the reduction in real-time within hours of the upgrade going live.
What is the Superchain and how does it affect bridging between OP-based L2s?
The Superchain is Optimism's vision for a network of L2s sharing the same OP Stack codebase, security model, and sequencing infrastructure. Members include Optimism, Base, Mode, Zora, and several others. Within the Superchain, cross-chain messaging uses the native OP Stack bridge mechanism — faster and cheaper than third-party bridges because the chains share underlying infrastructure. Bridging from Base to Optimism through the Superchain takes minutes rather than 7 days, at canonical bridge prices.
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