# `GSLayer metricsValue:forKey:`

*Instance Method*

Value described by a metrics key for a metric side.

## Declaration

```objc
- (CGFloat) metricsValue:(GSMetricNumbers) metric forKey:(NSString *) key;
```

```python
metricsValue_forKey_(metric: GSMetricNumbers, key: str) -> float
```

## Parameters

- `metric` — The metric side that the key is evaluated for.
- `key` — The metrics key to evaluate.

## Discussion

Returns `NSNotFound` when the key cannot be resolved.

## See Also

### Metric Values

- [`GSMetricNumbers`](/Core/GlyphsCore/GSMetricNumbers)
- [`GSLayer metricsValue:atHeight:`](/Core/GlyphsCore/GSLayer/metricsValue:atHeight:) — Metric value for a side at a measurement height.
- [`GSLayer metricsValue:forKey:value:atHeight:`](/Core/GlyphsCore/GSLayer/metricsValue:forKey:value:atHeight:) — Evaluates a metrics key for a metric side.