---
title: ulpOfOne
framework: swift
role: symbol
role_heading: Type Property
path: swift/floatingpoint/ulpofone
---

# ulpOfOne

The unit in the last place of 1.0.

## Declaration

```swift
static var ulpOfOne: Self { get }
```

## Discussion

Discussion The positive difference between 1.0 and the next greater representable number. ulpOfOne corresponds to the value represented by the C macros FLT_EPSILON, DBL_EPSILON, etc, and is sometimes called epsilon or machine epsilon. Swift deliberately avoids using the term “epsilon” because: Historically “epsilon” has been used to refer to several different concepts in different languages, leading to confusion and bugs. The name “epsilon” suggests that this quantity is a good tolerance to choose for approximate comparisons, but it is almost always unsuitable for that purpose. See also the ulp member property.