> For the complete documentation index, see [llms.txt](https://docs.agilefi.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.agilefi.org/getting-started/protocol-math/interpreting-exchange-rates.md).

# Interpreting Exchange Rates

The aToken [Exchange Rate](/atokens/exchange-rate.md) is scaled by the difference in decimals between the aToken and the underlying asset.

```javascript
const oneSTokenInUnderlying = exchangeRateCurrent / (1 * 10 ^ (18 + underlyingDecimals - aTokenDecimals))
```

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

```javascript
const aTokenDecimals = 8; // all aTokens have 8 decimal places
const underlying = new web3.eth.Contract(erc20Abi, batAddress);
const aToken = new web3.eth.Contract(aTokenAbi, sUsdcAddress);
const underlyingDecimals = await underlying.methods.decimals().call();
const exchangeRateCurrent = await aToken.methods.exchangeRateCurrent().call();
const mantissa = 18 + parseInt(underlyingDecimals) - aTokenDecimals;
const oneSTokenInUnderlying = exchangeRateCurrent / Math.pow(10, mantissa);
console.log('1 aUSDC can be redeemed for', oneSTokenInUnderlying, 'USDC');
```

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

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

```javascript
const underlyingTokens = aTokenAmount * oneSTokenInUnderlying
```


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