What is wei in crypto? The smallest unit of ether explained

Wei is the smallest unit of ether (ETH), the native currency of the Ethereum network: one ether equals 10^18 wei, or 1,000,000,000,000,000,000 wei. Ethereum uses wei internally so that every amount, from a large transfer to a tiny gas fee, can be counted in whole numbers.

Think of wei as Ethereum’s version of a cent, only far smaller. You rarely see it in an exchange app, but it sits underneath every ETH balance, every transaction fee and every smart contract on the Ethereum blockchain.

What is wei in crypto, in plain words?

Wei is the atomic unit of ether: an amount that can’t be divided any further. Where a euro splits into 100 cents and a bitcoin into 100 million satoshis, one ether splits into a billion billion wei.

Every ETH balance is stored as a number of wei. When your wallet shows 0.5 ETH, the Ethereum blockchain actually records 500,000,000,000,000,000 wei. The wallet simply divides by 10^18 to show you a readable number.

Smallest units compared

Wei is far smaller than the smallest unit of most other currencies:

That extra precision is why Ethereum, with its smart contracts and tiny fees, needed a much finer unit than Bitcoin.

Who is wei named after?

Wei is named after Wei Dai, a computer engineer and cryptographer from the cypherpunk movement of the 1990s. In 1998 he described b-money, an early proposal for anonymous, distributed digital cash that influenced later cryptocurrencies. Ethereum’s founders named the smallest unit of ether after him, just as Bitcoin’s smallest unit is named after its creator, Satoshi Nakamoto.

Other ether units carry names of cryptography pioneers too, such as szabo after Nick Szabo and finney after Hal Finney.

Ether units: the full table

Ethereum has a ladder of denominations, each 1,000 times bigger than the one before. Only three are commonly used: wei, gwei and ether.

So one gwei equals one billion wei, and one ether equals one billion gwei. Names such as mwei, szabo and finney are mostly found in developer tools and unit converters.

Why wei exists: precision without decimals

Wei exists because computers handle whole numbers more reliably than decimals. Ethereum’s virtual machine has no decimal numbers at all, so every amount must be a whole number of the fundamental unit.

That brings three benefits:

• Precise calculations. Rounding errors in decimals could create or destroy tiny amounts of money. Counting in wei avoids that, which matters when smart contracts move funds automatically.
• Tiny amounts. Gas fees, interest and token rewards can be very small. Wei gives enough precision to charge or pay fractions of a cent.
• Agreement. Whole-number maths gives the same result on every computer, so every node on the network agrees on each balance down to the last wei.

Developers see this directly in code. In Solidity, Ethereum’s main language, writing “1 ether” in a contract is shorthand for 10^18 wei, and every balance a contract reads comes back in wei.

Gwei: the most commonly used unit for gas prices

Gwei is the most commonly used unit in everyday Ethereum use, because it’s the unit for gas prices. When a wallet shows a gas price of 2 gwei, it means 2 billion wei for every unit of gas your transaction uses.

The gas price has two parts: the base fee, set by the network and burned, and an optional priority fee for the validator. Both are expressed in gwei but paid in wei behind the scenes. Our page on gwei covers gas prices in more detail.

Wei vs gas: what’s the difference?

Wei is a unit of money; gas is a unit of work. Gas measures how much computing effort a transaction needs: a simple ETH transfer uses 21,000 gas, while a token swap uses more. The gas price says how much you pay per unit of gas, in gwei or wei. Multiply the two and you get the fee: gas used × gas price = transaction fees in wei. So gas tells you how big the job is, and wei tells you what each unit of that job costs.

Converting wei: how to calculate gwei and ETH

Converting wei is a matter of moving the decimal point. Divide to go to a bigger unit; multiply to go to a smaller one.

• Wei to gwei: divide by 10^9 (one billion).
• Wei to ETH: divide by 10^18.
• ETH to wei: multiply by 10^18.
• Gwei to ETH: divide by 10^9.

A worked example: one Ethereum transaction

Here’s a gas fee calculation for a simple ETH transfer, which uses 21,000 units of gas, at a gas price of 2 gwei:

1. 21,000 gas × 2 gwei = 42,000 gwei.
2. 42,000 gwei × 1,000,000,000 = 42,000,000,000,000 wei.
3. 42,000,000,000,000 wei ÷ 10^18 = 0.000042 ETH.
4. If ether’s current price were €3,000, the fee would be 0.000042 × €3,000 = €0.126, about 13 cents.

A unit converter on any block explorer does these steps for you, but knowing the scale helps you spot a mistake.

Converting larger amounts

For bigger sums, the same rule applies. 2.5 ETH is 2,500,000,000,000,000,000 wei, and 0.01 ETH is 10,000,000,000,000,000 wei. If a raw ETH amount looks about 18 digits too long, you’re almost certainly looking at wei.

Where you’ll see wei as an investor

Most people never type a wei amount, but it shows up in a few places across the Ethereum ecosystem:

• Wallet fee screens show gwei for gas prices and convert the total into ETH and euros.
• Block explorers sometimes list raw values in wei, especially for smart contract calls.
• Token approvals can show very large whole numbers, because tokens are counted in their own smallest unit too. An ERC-20 token sets its own number of decimals, which is why a raw token amount can look huge.
• Exchange withdrawals are shown in ETH, but the network fee is charged in wei.

Why wei matters to you

Understanding wei won’t change what you pay, but it helps you avoid costly mistakes:

• Check the unit before you confirm. Mixing up wei, gwei and ETH by a factor of a billion is easy when you edit gas settings manually. When in doubt, leave the wallet’s suggested fee.
• Watch unlimited approvals. A huge number in an approval request usually means you are letting a contract spend all of that token. Only approve what you need, and only on apps you trust.
• Know there’s no undo. Ethereum transactions can’t be reversed, and in the EU no compensation scheme covers crypto losses from mistakes or scams.
• Keep records in ETH and euros. For tax purposes you need the euro value of fees and trades, not the wei amount. Your exchange or wallet history usually shows both ETH and euros.

The bottom line

Wei is the smallest denomination of ether: 10^18 wei make one ETH, and one billion wei make one gwei. It exists so Ethereum can count every balance and fee in whole numbers. Treat gwei as the unit for gas prices, ETH as the unit for balances, and wei as the plumbing underneath.

Related terms

• Gwei
• Ethereum
• Gas Fee
• Smart contract
• ERC-20