eth_getBlockTransactionCountByNumber

eth_getBlockTransactionCountByNumber reports how many transactions sit in a single Arbitrum One block, identified by its height or by a tag such as latest. Arbitrum One is an Optimistic Rollup (chain ID 42161) where the Nitro sequencer pays gas in ETH and posts batches down to Ethereum L1, so block occupancy reflects rollup demand rather than L1 mempool pressure. Send the request to https://arbitrum.therpc.io/YOUR_API_KEY and you get back the number of transactions in the block at the given height or block tag, encoded as a hex string.

Use cases

• Poll the latest block's transaction count to gauge real-time load on the Arbitrum sequencer during busy DeFi windows on GMX or Camelot.
• Build a per-block fullness time-series to feed fee-estimation heuristics that weigh L2 execution cost against L1 calldata posting cost.
• Walk a range of block numbers to flag near-empty blocks or unusually dense ones for throughput analysis.

Parameters

Response

Example request

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "eth_getBlockTransactionCountByNumber",
7    "params": ["latest"],
8    "id": 1
9  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• The pending tag counts transactions the sequencer currently holds for the next block; that figure shifts between calls as Arbitrum's sub-second soft confirmations land, so treat it as a moving estimate.
• The result is a hex string (e.g. "0x2a") — run it through parseInt(value, 16) before any numeric comparison.

Supported networks

• Mainnet — Chain ID: 42161
• Sepolia — Chain ID: 421614

See also

• eth_getBlockTransactionCountByHash
• eth_blockNumber
• eth_getBlockByNumber
• eth_getTransactionByBlockNumberAndIndex

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"eth_getBlockTransactionCountByNumber","params":[""]}'