# Limits consumption

Ahrefs API is available on [eligible paid plans](https://ahrefs.com/pricing). On all other plans, you'll still have access to a [limited set of free test queries](./free-test-queries.md).

All requests besides [free test queries](./free-test-queries.md) and the *Rank Tracker*, *Management*, *Public* and *some other* endpoints consume **API units**. If an endpoint is free, you'll see a note about that on its documentation page; otherwise, it consumes units.

The units consumption per request is calculated as follows:

```
max(base_cost, per_row_cost * num_rows)
```

The `base_cost` of each request is **50 units**. The `per_row_cost` is the sum of the costs of each unique field that appears in either the returned result, or in the `where` or `order_by` parameters. If a field appears in multiple parameters, it is counted once.

The default cost of a field is **1 unit**. However, certain metrics are more expensive and may consume **5** or **10 units**. Such exceptions are noted in the each endpoint's field description. Requests served from cache do not consume units.

Each API request indicates its units consumption behavior via the following response headers:

- `x-api-rows` The number of rows returned.
- `x-api-units-cost-row` The per-row units cost.
- `x-api-units-cost-total` The overall units that the request should consume based on the number of rows and per-row cost.
- `x-api-units-cost-total-actual` The overall units that the request actually consumed.
- `x-api-cache` Whether the request was served from cache. One of: `hit` `miss` `no_cache`

> **INFO**
> A good way to estimate the cost of a request is to run it with a [free target](./free-test-queries.md) and check the `x-api-units-cost-total` field value. To display the response headers when using the `curl` command, you can use the `-v` or `--verbose` option.

## Example 1

Consider a request to the *Site Explorer - Domain rating* endpoint (`/site-explorer/domain-rating`).

It does not accept a `select`, `where`, or `order_by` parameter, and it returns a single row containing two fields - `domain_rating` and `ahrefs_rank`, for a per-row cost of 2 units.

The total row cost (per-row cost multiplied by the number of rows) is less than the base cost. Therefore, this request costs the base amount of **50 units**.

## Example 2

Consider a more complex request to the *Site Explorer - Backlinks* endpoint (`/site-explorer/all-backlinks`), which allows the configuration of the `select`, `where`, and `order_by` parameters.

Suppose this request has two fields selected:
```
select=title,traffic
```
two fields in the filter expression:
```
where={"and":[{"field":"traffic","is":["gt",1000]},{"field":"refdomains_source","is":["gt",10]}]}
```
and an ordering field:
```
order_by=traffic:desc
```

Across these parameters, there are three unique fields, of which `title` and `refdomains_source` cost 1 unit each, while `traffic` costs 10 units. Thus, the per-row cost is 1 + 1 + 10 = 12 units.

Suppose the request returns 500 rows. Then, the total row cost (12 * 500 = 6000 units) exceeds the base cost. Therefore, the cost of this request is **6000 units**.