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all about Ether Units

How to assign an ether unit to a variable?

ether units can be assigned to any number in Solidity, but this number MUST be a literal number.

The following sub-demonimation of ether are available in Solidity, from the smallest to the largest: wei, finney, szabo and ether.

You can assign these keywords as suffix to a literal number in Solidity. Like for instance

500000 wei

3000 szabo

50 finney

3 ethers

Available ether units.

As mentioned in the previous section, these ether units are available in Solidity. The only effect of the sub-denomination suffix is a multiplication by a power of ten,

  • 1 wei = 1 * 10 ** 18 = 1_0
  • 1 szabo = 1 * 10 ** 6
  • 1 finney = 1 * 10 ** 3

By default, ether numbers / currencies (like msg.value) without a postfix are assumed to be wei.

These are the names of famous cryptographers who inspired or were involved in the early days of Bitcoin

Conversion table

  • 1 ether = 1,000,000,000,000,000,000 wei
  • 1 ether = 1,000,000 szabo
  • 1 ether = 1,000 finney
wei szabo finney ether
wei 1 0.000000000001 0.000000000000001 0.000000000000000001
szabo 1,000,000,000,000 1 0.001 0.000001
finney 1,000,000,000,000,000 1,000 1 0.001
ether 1,000,000,000,000,000,000 1,000,000 1,000 1

Quick tip for converting in your mind

This table and units might sound complex and confusing. Here is a simple way to remember: • Always start by counting in wei. • Remember the number of trailing zeros. 1 finney = 1e12 wei = 12 zeros 1 szabo = 1e15 wei = 15 zeros 1 ether = 1e18 wei = 18 zeros NB: You can also use etherconverter.online for quick conversion. It displays other units (like Kwei, Mwei (Shannon), Kether, etc…), but these units are not available in Solidity.

Working with variables and Ether Units

The code below is a really simple example of what a variable holding an ether value would look like.

uint256 price = 0.06 ether;
require(msg.value == price);

This other example below will assume that the message value represents 0.06 % of an Ether.

uint256 percentage = 6;
require(msg.value == 1 ether * percentage / 100);

Assertions and Comparisons with Ether units

2 ether == 2000 finney evaluates to true

assert(1 wei == 1);
assert(1 szabo == 1e12);
assert(1 finney == 1e15);
assert(1 ether == 1e18);

Using Ether units for percentages

The code below is a really simple example of what a variable holding an ether value would look like.

uint256 price = 0.06 ether;
require(msg.value == price);

This other example below will assume that the message value represents 0.06 % of an Ether.

uint256 percentage = 6;
require(msg.value == 1 ether * percentage / 100);

References