Glossary · Ethereum units

Finney

Published 28 Apr 2025 · Updated 20 Oct 2026 · 8 min read

A finney is a unit of ether (ETH) equal to 0.001 ETH, or 10¹⁵ wei, so 1,000 finney make one ether. Also called a milliether, it is named after Hal Finney, the software developer who received the first Bitcoin transaction. Wallets and code now mostly use ether, gwei and wei instead.

  • One finney equals 0.001 ether, or 10¹⁵ wei, so 1,000 of them make one ether.
  • The unit is named after Hal Finney, who received the first Bitcoin transaction in 2009.
  • The unit is rarely used today. Gas prices are quoted in gwei and balances in ether.
The ether denomination ladderWhere ether units show up in feesWriting ether amounts in SolidityWho Hal Finney wasHow the Finney attack worksHandling ether amounts in productsFinney FAQ

The ether denomination ladder

Each step is 1,000 times the previous unit, from wei to ether. Software on the Ethereum network stores and sends amounts as whole numbers of wei, the smallest unit. One ether contains 10¹⁸ wei. The 2014 whitepaper pre-labelled units "for convenience and to avoid future argument", citing Bitcoin's mBTC, uBTC and satoshi debate. The 2016 Homestead guide connects several names with figures from computer science and cryptoeconomics.

Figure 1 · Exact unit mathCompare seven ether unitsTry 1 ether, then 1 gwei, and compare the same amount across all seven denominations.
Exact: wei is the smallest unit
Unit
wei1,000,000,000,000,000,0001 wei · Wei is named after Wei Dai, who proposed b-money in 1998.
kweibabbage1,000,000,000,000,00010³ wei · Kwei is also called babbage, after Charles Babbage.
mweilovelace1,000,000,000,00010⁶ wei · Mwei is also called lovelace, after Ada Lovelace.
gweishannon1,000,000,00010⁹ wei · Gwei is also called shannon, after Claude Shannon.
szabomicroether1,000,00010¹² wei · Szabo, also called microether, honors Nick Szabo, known for the idea of smart contracts.
finneymilliether1,00010¹⁵ wei · Finney, also called milliether, is named after Hal Finney.
ether110¹⁸ wei · Ether is the main unit, used for ordinary amounts and balances.

Conversions use exact integer math in wei, and nothing is sent.

Where ether units show up in fees

Gas prices are quoted in the gwei unit, balances in ether, and code works in wei. A gas price is the cost of one gas unit, so the transaction fee also depends on gas used. At the YCharts daily average gas price of 0.67 gwei for 19 October 2026, a plain transfer cost about 0.014 finney. Etherscan showed a base fee of 0.039 gwei at 09:04 UTC on 20 October 2026, so a transfer with no tip cost 0.000819 finney.

EIP-1559 has been live since the London upgrade on 5 August 2021. The fee equals gas used × (base fee + priority fee). A plain ETH transfer uses 21,000 gas. In ethereum.org's example, that transfer at 10 gwei plus a 2 gwei tip costs 0.000252 ETH, or 0.252 finney. Of that, 0.21 finney is burned as the base fee and 0.042 goes to the validator as the priority fee. The base fee can change by at most 12.5% per block.

Figure 2 · Sample feesCalculate and split a feeChoose a transaction and a fee level, or set both fee parts yourself, to compare units and see the burn and the validator tip.
Transaction
Fee level
10 gwei
2 gwei
Fee in gwei252,000
Fee in finney0.252
Fee in ether0.000252
Burn iconBurned (base fee) 210,000 gweiNode iconTo the validator (priority fee) 42,000 gwei
21,000 gas × (10 + 2) gwei = 252,000 gwei = 0.252 finney

Token transfer and swap gas amounts are samples. Fees vary from block to block.

Writing ether amounts in Solidity

The Solidity compiler removed the finney and szabo suffixes in version 0.7.0 on 28 July 2020. The documentation says they were rarely used and did not make the actual amount readily visible. Solidity 0.6.11 had added gwei on 7 July 2020. Today a number in Solidity can take the suffix wei, gwei or ether. The sample shows the old literal next to the current forms.

Solidity · ether units
// Solidity 0.6 and earlieruint256 fee = 1 finney;      // removed in Solidity 0.7.0
// Solidity 0.7.0 and lateruint256 fee = 1e15 wei;      // the same amount, 0.001 etheruint256 tip = 2 gwei;uint256 deposit = 0.5 ether;

In Solidity 0.7.0 and later, write this amount as 1e15 wei or 0.001 ether. When updating older code, replace each removed denomination literal with an explicit value of the same size. Check the number of zeros.

Who Hal Finney was

Harold Thomas Finney II (4 May 1956 to 28 August 2014) was a software developer and cypherpunk. He worked on PGP at PGP Corporation until retiring in 2011. He built an early proof-of-work token system and believed he was the first person besides Satoshi Nakamoto to run the Bitcoin software.

  1. Early 1990s

    Privacy software and cypherpunks

    He was a regular contributor to the cypherpunks mailing list in the early 1990s. He was also the second developer on PGP, after Phil Zimmermann.

  2. August 2004

    Reusable proofs of work

    On 15 August 2004, he announced RPOW, or Reusable Proofs of Work, a hashcash-based server issuing signed tokens. He later called it "an attempt to create my own proof of work based currency".

  3. January 2009

    The first Bitcoin transfer

    On 12 January 2009, Satoshi Nakamoto sent him 10 BTC in block 170 as a test, the first Bitcoin transaction. He had posted "Running bitcoin" on 10 January 2009, Pacific time.

  4. February 2011

    A double-spend attack warning

    His bitcointalk post on 13 February 2011 laid out a miner's double spend. The example focused on goods handed over after an unconfirmed payment.

  5. August 2014

    Death and cryopreservation

    He died on 28 August 2014, after an ALS diagnosis in August 2009. He was cryopreserved by the Alcor Life Extension Foundation, based in Scottsdale, Arizona.

How the Finney attack works

Hal Finney described this miner-assisted double-spend attack on the bitcointalk forum on 13 February 2011. It targets merchants accepting zero-confirmation payments. An attacker mines a block transferring coins between two addresses they control, then withholds it. They pay a merchant with the same coins. After a few seconds, the merchant hands over the goods. The attacker releases the block, and the hidden transfer takes precedence over the merchant's payment.

Gemini notes that merchants who wait for block confirmations instead of accepting unconfirmed payments are not exposed to the basic attack. The Bitcoin Wiki adds that the risk cannot be eliminated, and the Vector76 variant can reverse a payment with one confirmation. bitcoin.org calls six confirmations the minimum for high-value transfers. The sources describe the attack for Bitcoin. Ethereum has used proof of stake since the Merge on 15 September 2022, and its blocks take about 15 minutes to finalize.

Figure 3 · Simplified Bitcoin exampleFollow the withheld blockStep through the payment sequence, then switch on confirmation waiting to see why the basic attack no longer pays.
Node iconAttacker's minerMines a block with tx A and keeps it private
Shop iconMerchantWaiting for a customer
Network iconBitcoin networkDoes not know the block
tx ACoins to the attackerHidden in a private block
tx BThe same coins to the merchantNot sent yet
Step 1 of 4 · Pre-mineThe attacker mines a block containing a transfer between two of their own addresses. They keep this block private instead of broadcasting it.

This simplified Bitcoin example illustrates the basic attack, not every double-spend variant.

Handling ether amounts in products

We build Ethereum apps, smart contracts, wallets, dApps, DeFi tools and NFT solutions. Our smart contract development work settles gas costs at design time, not at the end. We also offer blockchain consulting and audits. Amounts need the most care where they cross a boundary, between a form field, a library call, a contract and a screen. The five areas below connect stored values, fees and displayed amounts.

PixelPlex case icon

Our Ethereum development work includes gas usage optimization for Ethereum smart contracts, with over 15% savings on transaction fees thanks to contract optimization. The savings come from what the contract does on chain, not from the unit used to show the fee.

  1. Integer storage

    Keep contract amounts in whole wei. Treat that integer as the reference value when reviewing user inputs, stored amounts and outgoing transactions, even when displays use another denomination.

  2. Conversion boundaries

    ethers.js still parses "finney", but Solidity 0.7.0 and later rejects it as a suffix. Define which unit every input accepts and every output shows.

  3. Fee calculation

    Estimate gas use separately from the per-unit gas price. Show the base fee and priority fee as distinct parts of the estimate, with their units clearly labeled.

  4. Readable amounts

    Label displayed values with their units. Make the difference between a payment amount, a gas price and a total fee explicit wherever a user reviews a transaction.

  5. Amount and fee tests

    Test conversions and fee calculations against known values. Include older unit names in reviews of existing code, and verify that displayed amounts match the intended wei values.

Discuss amount handling in your Ethereum product

If unit handling or fee behavior in your product needs a review, we can help you plan the next steps.

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Finney FAQ

How much is one finney in ether?

One finney is 0.001 ether, so 1,000 finney make one ether. It is the same amount as one milliether. The 2014 whitepaper expected this unit to serve microtransactions. That never caught on, and gas prices are quoted in gwei and amounts in ether.

How many wei and gwei equal one finney?

One finney is 10¹⁵ wei (1,000,000,000,000,000 wei) and 1,000,000 gwei. It is also 1,000 szabo. Each named unit is 1,000 times the one below it. Moving one step up the ladder divides the number by 1,000 without changing the value.

Why is the ether unit called finney?

It is named after Hal Finney. The 2016 Homestead guide says several unit names honor "seminal figures" in computer science and cryptoeconomics without listing them. Later guides on ether units name him directly. He was an early PGP developer, the creator of RPOW and the recipient of the first Bitcoin transaction.

Is finney still supported in code?

Not in Solidity. Version 0.7.0 removed the finney and szabo suffixes in July 2020. Some tools still accept the name. ethers.js parses it, Vyper's as_wei_value accepts it, and the Etherscan converter lists it. viem and Foundry's cast to-unit work with ether, gwei and wei. web3.js still accepts it, but its repository was archived in March 2025.

What is the difference between gwei and finney?

One finney equals one million gwei. Gwei (10⁹ wei) is the unit for gas prices, while finney (10¹⁵ wei) is a larger unit that is rarely used. ethereum.org's own denomination table lists only wei and gwei. The Etherscan converter still offers it.

What is a Finney attack in Bitcoin?

It is a miner-assisted double spend aimed at merchants who release goods for payments that have no confirmation. Hal Finney described it on 13 February 2011. Gemini notes that merchants who wait for confirmations are not exposed to the basic attack, and reported in 2020 that there was no evidence of any major instances.

What else shares the name Finney?

The Finney attack, a Bitcoin double spend, is named after Hal Finney. So is the SIRIN LABS FINNEY smartphone, announced in 2017 and put on pre-order in November 2018. Bittensor's mainnet is also called "finney", though its documentation does not explain the name.

Related terms

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Sources (36)

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