Token Supply & Decimals Calculator

An ERC-20 contract keeps every balance as a plain integer. The decimals() value on the contract is a display hint and nothing else: 1 USDC is stored as 1000000 because USDC reports 6 decimals, while 1 DAI is stored as 1000000000000000000 because DAI reports 18. Assume the wrong one and a transfer is off by a factor of a trillion.

This calculator does the two sums that sit around that number. It converts a human amount into the base-unit integer a contract call takes, and back again, and it measures a holding against a total supply as a percentage, in basis points, as a “1 in N” figure, and as the raw integer totalSupply() returns. Every value is computed with BigInt, so a supply with 78 digits stays exact.

Getting Your First Base-Unit Value

1. Set Token decimals. The preset chips cover the common cases: 18 for ETH and most ERC-20s, 6 for USDC and USDT, 8 for WBTC, 9 for Solana SPL tokens, and 0 for a whole-unit token.
2. In the first panel, type an amount. With the direction on Display amount → base units, entering the bundled sample of 2500.75 returns 2500750000000000000000, which is the integer transfer(), approve() or mint() expects.
3. Press Swap to reverse the direction and turn a base-unit integer back into the amount a wallet shows.
4. Fill Total supply and Amount held in the second panel to see the share figures. The sample’s 2,500.75 against a 1,000,000,000 supply works out to 0.000250075% of supply, or roughly 1 token in 399,880.
5. Use the Copy button on any result box, including the raw totalSupply() integer.

How the Math Converts Amounts

• Display to base units: the amount is split at the decimal point, the fractional part is right-padded with zeros to exactly decimals digits, and the two parts are concatenated into one integer. No multiplication by a float ever happens.
• Base units to display: the integer is left-padded to at least decimals + 1 digits, then a point is placed decimals places from the right and trailing zeros are trimmed.
• Share of supply: both amounts are taken to base units first, so the ratio is one integer divided by another. The percentage is produced by scaling the numerator by 10¹² before dividing, which fixes the output at up to 12 fractional digits.

Precision: What Stays Exact and What Rounds

• Base-unit conversion is lossless in both directions for any size of number, because it is string surgery on integers rather than arithmetic on doubles.
• The percentage and basis-point figures are truncated, not rounded, at 12 fractional digits. For a holding of a few thousand tokens in a billion-token supply that is far more precision than the number is worth, but a dust holding in a large supply can show as 0.
• Decimals must be a whole number from 0 to 36. Anything outside that range is refused, and a display amount with more fractional digits than the token allows is rejected with “18 decimals allow at most 18 fractional digits; this amount has 19.”
• The base-units field only accepts a whole number. A value with a decimal point returns “Base units are a whole number, no decimal point, no sign.”