Blob Gas

Blob gas is the unit of computation required to post and temporarily store data blobs on the Ethereum blockchain, introduced via EIP-4844 (Proto-Danksharding). It is a separate fee market from the standard gas used for transaction execution and smart contract deployment. This separation allows the cost of posting large data batches—essential for Layer 2 rollups—to fluctuate independently, preventing competition and price spikes in the main execution gas market. Users pay blob gas fees in ETH when submitting transactions that include blob-carrying transactions.

The primary purpose of blob gas is to drastically reduce the cost for Layer 2 (L2) rollups like Optimism and Arbitrum to post their transaction data to Ethereum. Instead of storing this data permanently in calldata, which is expensive, rollups can post it to a new, dedicated blobspace for approximately 1/10th the cost. Each blob can hold up to ~128 KB of data and is stored by the consensus layer for a short, fixed period (currently 4096 epochs, or ~18 days), which is sufficient for all parties to verify and challenge L2 state transitions.

The blob gas market operates on a target-and-limit mechanism similar to EIP-1559. There is a per-block blob gas target (currently 3 blobs or 0.375 MB) and a blob gas limit (6 blobs or 0.75 MB). If blob usage is above the target, the fee increases; if below, it decreases. This base fee for blob gas is also burned, applying deflationary pressure to ETH. The design ensures blob space is reliably available for rollups at predictable, low costs, scaling Ethereum's data capacity without burdening the execution layer.

Blob gas is the fee unit used to pay for the temporary data storage and bandwidth of blobs—large data packets introduced by EIP-4844 to scale Layer 2 rollups. Unlike standard execution gas for computation, blob gas is priced by a separate, dedicated fee market and is consumed when a transaction includes one or more blobs in its blob-carrying transaction type. This separation prevents competition for block space between execution and data availability, creating a more stable and predictable cost environment for rollup data posting.

The blob gas fee market operates on a target-and-limit system. Each Ethereum block has a blob gas limit (currently targeting 3 blobs per block, or 0.375 MB) and a target of 2 blobs. A base fee for blob gas adjusts dynamically block-by-block based on the utilization of blob space relative to this target, using a mechanism similar to EIP-1559. If blob usage exceeds the target, the base fee increases exponentially; if it's below, the fee decreases. This ensures blob space is used efficiently and prevents long-term congestion.

A critical feature of blob gas economics is its scarcity mechanism. The total blob gas limit per block is designed to grow slowly but is intentionally kept low to ensure the data can be widely propagated and stored by the network's nodes only for a short, fixed period (approximately 18 days). This temporary storage, enabled by blob-carrying transactions, is sufficient for Layer 2s to verify data availability but prevents the permanent state bloat associated with calldata, making it vastly cheaper.

From a user or rollup operator's perspective, the cost of a blob transaction has two components: the standard execution gas fee (for processing the transaction's main body) and the blob gas fee (for the attached data). The blob gas fee itself is calculated as blob_gas_used * blob_base_fee, where blob_gas_used is fixed per blob. This cost is then burned (EIP-1559 style), removing ETH from circulation, while the priority fee for the block builder is paid only on the execution component.

The introduction of blob gas fundamentally changes Ethereum's capacity model. By creating a dedicated data availability lane with its own pricing, it reduces the cost for Layer 2 rollups like Optimism and Arbitrum to post their transaction data by orders of magnitude. This cheaper, high-volume data pipeline is the core scaling mechanism of proto-danksharding, setting the stage for a future where full danksharding can further increase blob capacity across multiple data lanes.

EIP-4844, known as Proto-Danksharding, was a major Ethereum upgrade implemented in March 2024 as part of the Dencun hard fork. Its primary innovation was the introduction of blob-carrying transactions, which provide a new, low-cost data channel for Layer 2 rollups. By separating data posting from execution, EIP-4844 dramatically reduced transaction fees for rollup users while laying the foundational architecture—blobs, a separate blob gas market, and blobspace—required for the network's long-term scaling roadmap.

The upgrade was a direct response to the high and volatile cost of using CALLDATA, the previous method rollups used to post transaction data on-chain for security. CALLDATA is processed by every Ethereum node forever, creating permanent storage costs. EIP-4844's blobs, in contrast, are large data packets (~128 KB each) that are only stored by consensus nodes for a short period (approximately 18 days) before being pruned. This temporary storage model is the key to achieving scalable data availability without bloating the chain's permanent state.

A core component of EIP-4844 is the independent blob gas market. Unlike the gas used for execution (gas), blob gas is priced by a dedicated EIP-1559-style fee market that targets three blobs per block. This separation prevents competition between execution and data availability, ensuring rollup data posting has predictable costs. The fee mechanism dynamically adjusts based on demand for blobspace, burning excess fees to regulate supply.

The architecture introduced by Proto-Danksharding is explicitly designed for evolution. The term "proto" indicates it is the prototype for full Danksharding, a future upgrade that will expand capacity to 16 MB per slot and distribute blob data across a committee of validators. EIP-4844's successful deployment validates the core concepts and allows the ecosystem to build tooling and infrastructure, creating a smooth pathway for this next leap in scalability.

The immediate impact of EIP-4844 was a radical reduction in Layer 2 transaction fees, often by an order of magnitude or more, making applications on networks like Arbitrum, Optimism, and Base significantly more affordable. Beyond cost, it cemented Ethereum's rollup-centric roadmap by providing a dedicated, scalable highway for data, ensuring the L2 ecosystem can grow without congesting the base layer's execution block space.