Compute the Ethereum blob base fee from excess blob gas (or enter it directly), price a Layer 2 rollup transaction posted via a blob, and compare the cost against the old pre-Dencun calldata method.
How the model works
| Step | Formula |
|---|
| Blob base fee (wei) | MIN_BLOB_BASE_FEE (1) × e^(excess_blob_gas ÷ BLOB_BASE_FEE_UPDATE_FRACTION) |
| Usable bytes / blob | 4096 field elements × 31 bytes = 126,976 bytes |
| Cost per blob | blob base fee (wei) × 131,072 gas ÷ 1e18 × ETH price |
| Cost per rollup tx | (bytes per tx ÷ 126,976) × cost per blob |
| Blobs needed / day | (tx/day × bytes/tx) ÷ 126,976 |
| Pre-4844 calldata cost / tx | bytes per tx × 16 gas × L1 base fee (gwei) ÷ 1e9 × ETH price |
The exponential blob-fee formula is the EIP-4844 spec's continuous approximation of its integer "fake_exponential" reference implementation — accurate to a fraction of a percent for BLOB_BASE_FEE_UPDATE_FRACTION values this large. Pectra (EIP-7691) raised the target from 3 to 6 blobs/block and the fraction from 3,338,477 to 5,007,716; pick the fork above to match the network state you're modeling. Calldata is priced at 16 gas/byte (the standard non-zero-byte rate), which is the pre-Dencun method L2s used before blobs existed.
FAQ
What is the EIP-4844 blob base fee?
A separate fee market from regular gas, introduced by the March 2024 Dencun upgrade, that prices "blobs" — the large data chunks Layer 2 rollups use to post transaction data. It's computed as 1 wei × e^(excess_blob_gas ÷ BLOB_BASE_FEE_UPDATE_FRACTION).
What is excess_blob_gas?
A running counter in the block header that rises when blocks include more blobs than the target and falls when they include fewer. It drives the exponential fee formula, so sustained demand above target makes fees rise quickly.
Why are blobs cheaper than calldata?
Calldata costs 16 gas/byte in the main execution fee market; blob data costs a flat rate in its own, usually far less congested, market — a structural ~16x floor that's often much larger in practice since blob fees frequently sit near their 1 wei floor.
How much data fits in one blob?
126,976 usable bytes (4096 field elements × 31 bytes each) out of a 131,072-byte (128 KB) blob — one byte per 32 is reserved because field elements must stay under the BLS12-381 scalar modulus.
What did Pectra change?
EIP-7691 raised the target from 3 to 6 blobs/block and the max from 6 to 9, and increased BLOB_BASE_FEE_UPDATE_FRACTION from 3,338,477 to 5,007,716 so the fee's sensitivity stayed similar despite the higher target.
Does this call any real contracts?
No — it's a pure client-side model using your inputs or the preset scenarios; nothing is sent to an RPC node or a wallet.