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What a WU is

A WU is the unit of Node API usage. Your plan’s quota and its read limit are counted in WU. A call costs WU according to the size of the node’s answer: the more data the node returns, the more work it did. Most calls — an account, its resources, a contract call, building or broadcasting a transaction — cost 1 WU. Every answered call tells you its cost: the X-Node-API-WU response header over HTTP, the x-node-api-wu trailing metadata over gRPC. The dashboard shows your usage by day.

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The formula

  • KB — the size of the node’s answer in kilobytes (bytes ÷ 1024), before compression. gzip saves traffic, not WU.
  • round — to the nearest whole number; halves round up.
  • factor — depends on the kind of call:
The same rules apply to /walletsolidity/* and to gRPC, where the answer is measured in protobuf and the gRPC twins of these methods (GetNowBlock2, GetBlockByNum2, GetBlock, …) count as the same kinds of call. With factor 1, answers up to about 34 KB cost 1 WU.

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Fresh blocks

A block within 20 of the head of the network — about the last minute — costs a flat 3 WU, and its receipts 2 WU, whatever their size. A block that has not been produced yet costs what its (empty) answer costs: 1 WU. Older blocks and their receipts are charged by the formula. Ranges (getblockbylimitnext, getblockbylatestnum) are always charged by the formula, on the whole answer, and return at most 10 blocks per call.

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Measured examples

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What costs nothing

  • Refusals. A request refused with an error code (see Limits and errors) is not charged and carries no X-Node-API-WU.
  • A method the node does not have — 404 method_not_found, with X-Node-API-WU: 0. It still counts as one call against your per-second limit, so a loop of typos is slowed down, not billed.
  • No answer from the node — 502 node_error.
An error the node itself returns is an answer: java-tron reports most errors as JSON ({"Error": "…"}), often with status 200, and they are charged by size like any answer — at least 1 WU.

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Estimating your usage

  • Following every block of the chain — the header (1 WU) plus the receipts of the fresh block (2 WU) — is 3 WU per block: about 86,400 WU a day, or about 2.6M WU in 30 days.
  • A USDT transfer built and broadcast through the node is 2 WU.
  • Reading old blocks is the expensive part: an old block of 600–800 KB is 13–17 WU.
Quota is spent by WU; the per-second limits are counted per class of call — read WU per second, block calls per second, broadcasts per second. See Limits and errors and the numbers for each plan in Plans and billing.