Evm Token Decimals

EVM Token Decimals

Silent decimal mismatches are one of the easiest ways to ship balances or USD values that are off by orders of magnitude without throwing an error.

When to Use

• Reading ERC-20 balances in Python, TypeScript, or Solidity
• Calculating fiat values from on-chain balances
• Comparing token amounts across multiple EVM chains
• Handling bridged assets
• Building portfolio trackers, bots, or aggregators

How It Works

Never assume stablecoins use the same decimals everywhere. Query decimals() at runtime, cache by (chain_id, token_address), and use decimal-safe math for value calculations.

Examples

Query decimals at runtime

from decimal import Decimal
from web3 import Web3

ERC20_ABI = [
    {"name": "decimals", "type": "function", "inputs": [],
     "outputs": [{"type": "uint8"}], "stateMutability": "view"},
    {"name": "balanceOf", "type": "function",
     "inputs": [{"name": "account", "type": "address"}],
     "outputs": [{"type": "uint256"}], "stateMutability": "view"},
]

def get_token_balance(w3: Web3, token_address: str, wallet: str) -> Decimal:
    contract = w3.eth.contract(
        address=Web3.to_checksum_address(token_address),
        abi=ERC20_ABI,
    )
    decimals = contract.functions.decimals().call()
    raw = contract.functions.balanceOf(Web3.to_checksum_address(wallet)).call()
    return Decimal(raw) / Decimal(10 ** decimals)

Do not hardcode 1_000_000 because a symbol usually has 6 decimals somewhere else.

Cache by chain and token

from functools import lru_cache

@lru_cache(maxsize=512)
def get_decimals(chain_id: int, token_address: str) -> int:
    w3 = get_web3_for_chain(chain_id)
    contract = w3.eth.contract(
        address=Web3.to_checksum_address(token_address),
        abi=ERC20_ABI,
    )
    return contract.functions.decimals().call()

Handle odd tokens defensively

try:
    decimals = contract.functions.decimals().call()
except Exception:
    logging.warning(
        "decimals() reverted on %s (chain %s), defaulting to 18",
        token_address,
        chain_id,
    )
    decimals = 18

Log the fallback and keep it visible. Old or non-standard tokens still exist.

Normalize to 18-decimal WAD in Solidity

interface IERC20Metadata {
    function decimals() external view returns (uint8);
}

function normalizeToWad(address token, uint256 amount) internal view returns (uint256) {
    uint8 d = IERC20Metadata(token).decimals();
    if (d == 18) return amount;
    if (d  {
  const token = new Contract(tokenAddress, ERC20_ABI, provider);
  const [decimals, raw] = await Promise.all([
    token.decimals(),
    token.balanceOf(wallet),
  ]);
  return formatUnits(raw, decimals);
}

Quick on-chain check

cast call  "decimals()(uint8)" --rpc-url 

Rules

• Always query decimals() at runtime
• Cache by chain plus token address, not symbol
• Use Decimal, BigInt, or equivalent exact math, not float
• Re-query decimals after bridging or wrapper changes
• Normalize internal accounting consistently before comparison or pricing

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: affaan-m
• Source: affaan-m/ECC
• License: MIT
• Homepage: https://ecc.tools

Install and usage instructions live in the source repository linked above.