# Use Custom Weights

Here, you'll learn how to use the weights in your pallet from the output of benchmarking your pallet's extrinsics. It assumes that you have a file in your pallet's directory called `weights.rs`, containing the auto generated weights from running FRAME's benchmarking tool.

### Goal

Use weights generated by [FRAME's benchmarking tool](https://paritytech.github.io/substrate/master/frame_benchmarking/macro.benchmarks.html) in the extrinsics of your pallet.

### Use Cases

Using accurate weights generated from benchmarking for a pallet's extrinsics.

### Steps

#### 1. Define the `WeightInfo` trait in your pallet's `weight.rs` file

In order to use the `weights.rs` file generated by the benchmarking tool in your pallet (an example of Substrate [`pallet-example` weights here](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/examples/basic/src/weights.rs)), define a trait that will make it easy to access its functions. For example:

`pallets/example/src/weights.rs`

```rust
pub trait WeightInfo {
  fn example(len: usize,) -> Weight;
}
```

#### 2. Include `WeightInfo` in your pallet

In your pallet's `lib.rs`, declare `pub mod weights;` at the top and introduce `pub use crate::weights::WeightInfo;` to expose the `WeightInfo` trait to your pallet. Then, introduce a `WeightInfo` type into the `Config` trait of your pallet:

`pallets/example/src/lib.rs`

```rust
pub mod weights;
pub use weights::*;

// -- snip --

pub trait Config: frame_system::Config {
    // -- snip --

    /// Information on runtime weights.
    type WeightInfo: WeightInfo;
}
```

#### 3. Write the custom weight declaration

For each of your dispatchables, introduce an appropriate weights line to determine the weight using the configured `WeightInfo` type. For example, `T::WeightInfo::example` would be the weight function returned from `weights.rs` for the `example` extrinsic:

`pallets/example/src/lib.rs`

```rust
#[pallet::weight(T::WeightInfo::example(x.len()))]
fn example(origin: OriginFor<T>, arg: Vec<u32>) -> DispatchResult {
  // -- snip --
}
```

#### 4. Define the `WeightInfo` type in `Config` trait impls

You'll need to define the `WeightInfo` trait in both your pallet's tests mockup `mock.rs` and your Substrate `node`'s runtime.

In your pallet's `Config` trait impl in `mock.rs`, introduce the following line to exclude weights in our testing.

In `pallets/example/src/mock.rs` or `pallets/example/src/test.rs`:

```rust
impl Config for TestRuntime {
  // -- snip --
  type WeightInfo = ();
}
```

In your pallet's `Config` trait impl in `runtime/src/lib.rs`, introduce the following line to include weights in our runtime.

```rust
impl pallet_example::Config for Runtime {
  // -- snip --
  type WeightInfo = pallet_example::weights::SubstrateWeight<Runtime>;
}
```

Once you recompile your node, your extrinsic will now be using the custom weights defined in `pallets/example/src/weights.rs`.

### Examples

* [Benchmarking in the Example pallet](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/examples/basic/src/benchmarking.rs)
* [Weights in the Example pallet](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/examples/basic/src/weights.rs)

### Related material

* [Benchmarking](https://docs.infrablockchain.net/infrablockchain-docs/infrablockchain/tutorials/test/benchmark)
* [Calculate fees](https://docs.infrablockchain.net/infrablockchain-docs/infrablockchain/learn/substrate/learn/runtime-development/weights/calculate-fees)
* [Add benchmarks](https://docs.infrablockchain.net/infrablockchain-docs/infrablockchain/learn/substrate/learn/runtime-development/weights/add-benchmarks)