# Understanding OP\_SIZE

<figure><img src="/files/tF5YdtLfnchM1dXOTxWw" alt=""><figcaption></figcaption></figure>

**OP\_SIZE** measures the byte length of the top stack item and pushes that length as a new item. Unlike OP\_DEPTH which counts items, OP\_SIZE measures **data size** in bytes.

#### Basic Operation

```
Stack: <data> (where data = 0x11223344, 4 bytes)
OP_SIZE
Stack: <data> 4
```

The number **4** appears because the **data is 4 bytes long**. Crucially, **the original data remains** on the stack—OP\_SIZE duplicates length information without consuming the data.

**Key insight:** OP\_SIZE tells you "how big is this item" without removing or modifying the item itself.

<figure><img src="/files/SLkuMlBNdDcLo9ALJIpK" alt=""><figcaption></figcaption></figure>


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