Interpreting Exchange Rates

The sToken Exchange Rate is scaled by the difference in decimals between the sToken and the underlying asset.

const oneSTokenInUnderlying = exchangeRateCurrent / (1 * 10 ^ (18 + underlyingDecimals - sTokenDecimals))

Here is an example of finding the value of 1 cBAT in BAT with Web3.js JavaScript.

const sTokenDecimals = 8; // all sTokens have 8 decimal places
const underlying = new web3.eth.Contract(erc20Abi, batAddress);
const sToken = new web3.eth.Contract(sTokenAbi, sUsdcAddress);
const underlyingDecimals = await underlying.methods.decimals().call();
const exchangeRateCurrent = await sToken.methods.exchangeRateCurrent().call();
const mantissa = 18 + parseInt(underlyingDecimals) - sTokenDecimals;
const oneSTokenInUnderlying = exchangeRateCurrent / Math.pow(10, mantissa);
console.log('1 sUSDC can be redeemed for', oneSTokenInUnderlying, 'USDC');

There is no underlying contract for ETH, so to do this with sETH, set underlyingDecimals to 18.

To find the number of underlying tokens that can be redeemed for sTokens, multiply the number of sTokens by the above value oneSTokenInUnderlying.

const underlyingTokens = sTokenAmount * oneSTokenInUnderlying