# Why Do Web3 Applications Need BigNumber?

By [@0xhenrydev](https://paragraph.com/@0xhenrydev) · 2025-05-22

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**How Should We Handle Precision Issues in JavaScript?**

#### 🧠 Background: JavaScript Precision Limitation

JavaScript's native `Number` type is a **64-bit floating point** number (IEEE 754). This limits its **integer precision to 2^53 - 1**, or about **9e15**. Beyond that, numbers get rounded and lose accuracy.

    console.log(Number.MAX_SAFE_INTEGER); // 9007199254740991
    console.log(9007199254740991 + 1);    // 9007199254740992 ✅
    console.log(9007199254740991 + 2);    // 9007199254740992 ❌ precision loss
    

#### 💰 Why This Is a Problem in Web3

*   Ethereum (and other EVM chains) use `wei` as the smallest unit of ETH.
    
*   `1 ETH = 10^18 wei` → sending just 1 ETH involves manipulating a **big integer**, far beyond JS safe integer range.
    
*   Smart contracts return values in `wei`, making it unsafe to use regular `Number` for balances, gas, token supply, etc.
    

#### ✅ Solution: Use `BigNumber` or `BigInt`

To safely handle large numbers in Web3 apps, you must use **arbitrary-precision number types**, like:

*   `ethers.BigNumber` (from `ethers.js`)
    
*   `BigNumber.js` (arbitrary precision lib)
    
*   Native `BigInt` (ES2020)
    
*   `web3.utils.BN` (if using web3.js)
    

Example (using `ethers.js`):

    import { parseEther, formatEther } from 'ethers'; 
    const amountInWei = parseEther('1.0'); // returns BigNumber of 10^18 console.log(amountInWei.toString()); // '1000000000000000000' 
    const readable = formatEther(amountInWei); // back to human-readable ETH console.log(readable); // '1.0'
    

#### 🧪 Common Pitfall: Converting BigNumber to JS Number

Avoid this unless you're 100% sure the value is within the safe range:

    const unsafe = BigNumber.from("1000000000000000000"); console.log(unsafe.toNumber()); // May throw or round incorrectly if too large
    

Instead, use:

    console.log(unsafe.toString()); // Safe
    

#### 💡 When to Use `BigInt`?

If you don’t need compatibility with libraries like `ethers.js`, and you’re just doing arithmetic:

    const a = BigInt("1000000000000000000"); 
    const b = BigInt("3000000000000000000"); 
    const c = a + b; 
    console.log(c.toString()); // "4000000000000000000"
    

But be careful: **BigInt ≠ Number**, and you can’t mix them.

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### 🧩 Summary: Why `BigNumber` is Essential in Web3

ReasonExplanation✅ PrecisionJS `Number` can't represent large `wei` values accurately💡 CompatibilityWeb3 libraries return balances and values as `BigNumber`🔒 SafetyPrevent silent rounding bugs in balances, gas, etc.🛠️ ToolsUse `parseEther`, `formatUnits`, `BigNumber.from`, etc.

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*Originally published on [@0xhenrydev](https://paragraph.com/@0xhenrydev/why-do-web3-applications-need-bignumber)*