Blob Gas

Blob gas is the unit of pricing for posting large, temporary data packets called blobs on the Ethereum blockchain, introduced via EIP-4844 (Proto-Danksharding). Unlike standard gas used for computation and permanent storage, blob gas is specifically designed to be a low-cost resource for Layer 2 (L2) rollups (like Optimism and Arbitrum) to post their transaction data, enabling cheaper transaction fees for end-users. This mechanism operates on a separate, independent fee market, preventing competition between blob data and standard Ethereum transactions for block space.

The core innovation is the blob-carrying transaction, which includes a reference to a blob—a large data packet (~128 KB) stored off-chain in the Beacon Node consensus layer for a short period (approximately 18 days). This temporary storage, rather than permanent on-chain storage, is the key to reducing costs. The blob gas price is determined by a dedicated EIP-1559-style fee market, with a base fee that adjusts per block based on network demand for blob space and a priority fee for validator tips. Excess blob gas is burned, similar to the base fee burn for standard transactions.

For developers and users, the primary impact is dramatically reduced data availability costs for L2s. Before blobs, rollups posted their data as expensive calldata on the main Ethereum chain. By providing a dedicated, low-cost data channel, blob gas allows L2s to pass on significant fee savings. This is a foundational step toward the long-term vision of Danksharding, which will scale blob capacity further. Understanding blob gas is essential for analyzing L2 economics and the evolving architecture of Ethereum's scalability roadmap.

Blob gas is the fee paid to post and temporarily store large data packets, known as blobs, on the Ethereum blockchain as part of the EIP-4844 (Proto-Danksharding) upgrade. Unlike standard gas, which pays for execution and storage, blob gas is a separate fee market specifically for securing data availability—ensuring transaction data is published and accessible for a short period. This separation prevents competition for block space between execution and data, allowing Layer 2 rollups to post data more cheaply and predictably.

The blob gas market operates with its own base fee, which adjusts dynamically based on network demand for blob space, following an algorithm similar to EIP-1559. Each Ethereum block has a target of 3 blobs and a maximum of 6 blobs (as of the initial implementation). When blob usage exceeds the target, the base fee increases; when it's below, the fee decreases. This blob base fee is burned (removed from circulation), while a priority fee can be included for validators to incentivize faster inclusion, mirroring the main transaction fee structure.

A key design feature is the blob-carrying transaction, a new type that includes a standard execution payload and one or more blobs. The gas cost for the execution portion is calculated normally, while the blob data is priced separately using the blob gas market. Blobs are large (~128 KB each) but are not permanently stored in Ethereum's execution state; they are held by validators and consensus nodes for approximately 18 days (4096 epochs) before being pruned, which is sufficient for all Layer 2 networks to verify and challenge transactions.

The primary purpose of this system is to drastically reduce the cost for rollups (like Optimism and Arbitrum) to post their transaction data to Ethereum. By creating a dedicated, high-capacity data channel with its own fee dynamics, blob gas decouples data availability costs from the volatile mainnet gas fees. This makes Layer 2 transaction fees significantly cheaper and more stable, directly scaling Ethereum's capacity without compromising decentralization or security.

From a user's perspective, blob gas is typically abstracted away. When interacting with a Layer 2, the user pays a fee in the rollup's native token, which the rollup's sequencer uses to cover the blob gas cost when posting data batches to Ethereum. Developers working directly with blob-carrying transactions must account for two separate gas limits and fee calculations: one for execution and one for the attached blobs, using the current blob base fee provided by the network.

Blob gas is a specialized fee mechanism introduced in Ethereum's Dencun upgrade (EIP-4844) to price and manage temporary data storage for layer-2 rollups. Unlike standard gas, which pays for computation and permanent storage, blob gas is consumed to post large "blobs" of data—binary large objects containing transaction data from rollups like Optimism and Arbitrum—to a new, separate data layer. This data is stored for approximately 18 days, a period sufficient for fraud proofs and data availability sampling, after which it is automatically pruned by nodes to prevent state bloat. The key innovation is the creation of a distinct, variable gas market for this temporary data, decoupling its cost from the volatile demand for Ethereum's main execution layer.

The evolution of blob gas was a direct response to the unsustainable cost model for rollups prior to Dencun. Previously, rollups posted their compressed transaction data as calldata on the main Ethereum chain, a process that consumed expensive, permanent storage and competed directly with regular transactions for block space. This made scaling via rollups economically inefficient during periods of high network congestion. EIP-4844's proto-danksharding design introduced blobs as a data availability solution, providing a dedicated, lower-cost data highway. The gas pricing for blobs uses a separate base fee that adjusts independently via a dedicated target and maximum per block, creating a more predictable and scalable cost structure for rollup operators.

The implementation of blob gas represents a critical step toward Ethereum's full danksharding roadmap. While proto-danksharding provides 3-6 blobs per block, the long-term vision involves scaling this to 64+ blobs, massively increasing data bandwidth. The temporary storage model is essential for this future scale, as it allows nodes to efficiently manage data without the permanent burden of historical blobs. By establishing a new transaction type (TransactionType=3) and a new fee market, Ethereum has created the foundational architecture for a modular blockchain design, where execution, consensus, and data availability are optimized as separate layers. This evolution directly enables cheaper transaction fees on layer-2 networks, making Ethereum scaling more accessible and sustainable.

Blob gas is a distinct fee mechanism introduced in EIP-4844 to price and limit the data space used by blob-carrying transactions. It operates in parallel to the standard execution gas system but is priced via a separate, dedicated fee market. This separation prevents competition for block space between execution and data availability, ensuring that blob data costs do not directly inflate the cost of simple transfers or smart contract interactions. The unit of consumption is the blob, with each transaction able to carry up to six blobs, where one blob provides approximately 128 KB of data availability.

The blob gas price is determined by a target and maximum system per block. The protocol targets 3 blobs per block (0.375 MB) but allows a maximum of 6 blobs (0.75 MB). Similar to EIP-1559's base fee, the blob base fee adjusts dynamically based on whether the previous block's blob usage was above or below the target. If usage exceeds the target, the price increases exponentially; if below, it decreases. This creates a predictable, market-driven cost for data availability while enforcing a hard cap on network throughput for blob data.

A critical feature of blob gas is its ephemeral storage. Data in blobs is not accessible to the Ethereum Virtual Machine (EVM) and is only stored by consensus nodes and dedicated data availability sampling networks for a short period—currently 4096 epochs (approximately 18 days). After this window, the data can be pruned. This temporary commitment is secured by KZG polynomial commitments, which allow nodes to verify the availability and correctness of the data without storing it long-term, dramatically reducing the historical data burden on nodes.

From a user's perspective, when submitting a blob transaction, they pay two separate gas fees: execution gas for the EVM operations (like a normal transaction) and blob gas for the data carried in the blobs. Both fees are burned (destroyed) as part of Ethereum's fee-burn mechanism. This design ensures that the cost of providing scalable data for Layer 2 rollups is borne by the users of those rollups, without imposing permanent storage costs or excessive fee volatility on the core Ethereum network.