> For the complete documentation index, see [llms.txt](https://docs.getblock.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.getblock.io/api-reference/bitcoin-btc/bitcoin-blockbook-websocket-api/estimatefee-bitcoin.md).

# estimateFee - Bitcoin

Example code for the estimateFee WebSocket method. Complete guide on how to use the estimateFee WebSocket method in the GetBlock Web3 documentation.

Returns the backend fee estimate for one or more confirmation targets. Supplying the transaction's virtual size returns the estimated total fee for a transaction of that size, alongside the per-unit rate. This is the WebSocket form of the REST [api/v2/estimatefee](/api-reference/bitcoin-btc/bitcoin-blockbook-rest-api/api-v2-estimatefee-bitcoin.md) endpoint.

## Parameters

| Parameter | Type   | Required | Description                                                                   |
| --------- | ------ | -------- | ----------------------------------------------------------------------------- |
| blocks    | array  | Yes      | Confirmation targets in blocks, one estimate returned per entry               |
| specific  | object | No       | Chain-specific options: `conservative` for smart fee mode, `txsize` in vbytes |

## Message

{% code overflow="wrap" %}

```bash
wscat -c wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>

# then send:
{
    "id": "getblock.io",
    "method": "estimateFee",
    "params": {
        "blocks": [1, 6, 24],
        "specific": {
            "conservative": true,
            "txsize": 144
        }
    }
}
```

{% endcode %}

## Response

```json
{
    "id": "getblock.io",
    "data": [
        {
            "feePerTx": "171",
            "feePerUnit": "1190"
        },
        {
            "feePerTx": "74",
            "feePerUnit": "511"
        },
        {
            "feePerTx": "40",
            "feePerUnit": "278"
        }
    ]
}
```

## Response Fields

| Field      | Type   | Description                                                                |
| ---------- | ------ | -------------------------------------------------------------------------- |
| feePerTx   | string | Estimated total fee in satoshis for a transaction of the supplied `txsize` |
| feePerUnit | string | Estimated fee rate in satoshis per **kilobyte**, not per vbyte             |

Results are returned in the same order as the requested `blocks` targets.

{% hint style="warning" %}
`feePerUnit` is quoted per 1000 bytes, following the backend's `estimatesmartfee`, which reports BTC per kilobyte. Dividing by 1000 gives the sat/vB rate wallets usually display: the `1190` above is **1.19 sat/vB**, not 1190. Treating it as sat/vB overpays by three orders of magnitude.

`feePerTx` is derived as `txsize × feePerUnit / 1000`. In the response above, `144 × 1190 / 1000 = 171`.
{% endhint %}

## Use Cases

* **Fee Selection**: Choose a rate matching the confirmation speed a payment needs
* **Cost Preview**: Show the user the fee before signing
* **Tiered Options**: Offer fast, standard, and economy targets from one call
* **Batch Planning**: Size a consolidation against the current rate

{% hint style="info" %}
`feePerTx` is only meaningful when `txsize` is supplied. Without it, size the fee as `vsize × feePerUnit / 1000`, keeping the per-kilobyte denominator in mind.
{% endhint %}

## Error Handling

| Error                     | Message        | Description                                       |
| ------------------------- | -------------- | ------------------------------------------------- |
| error                     | Invalid params | The blocks array is missing or malformed          |
| 403 / RBAC: access denied | Access denied  | The GetBlock access token is missing or incorrect |