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Measurement framework ounces in cup question

Forums > Swift

Why does the Measurement framework not return exactly 8 fluid ounces when I convert one cup? I can't seem to find any reference (in or out of Apple's developer documentation) for a volumetric cup not equaling exactly 8 fluid ounces.

import SwiftUI

let testOneCup = Measurement(value: 1, unit: UnitVolume.cups)
let testOunces = testOneCup.converted(to: UnitVolume.fluidOunces)

It prints: 8.11537356078922 fl oz


Well, it seems that the Unitvolume.cups is a "legal cup" which is indeed 8.11537 ounces. It seems that a "legal cup" is a cup that in the US is used for nutritional values such as shown on a food label. Odd.


Just swinging back to post my "SOLUTION" if you will:

Per Apple's UnitVolume documentation, the .cups Unit has a coefficient of 0.24 (base is Liters for all UnitVolume unit types) and .fluidOunces has a coefficient of 0.0295735, I simply multiplied 0.0295735 * 8 (i.e., one ounce times eight), I created a custom unit (symbol: cupsUSKitchen) and gave it a coeffient of 0.236588 and that did the trick.

import SwiftUI

let cupsUSKitchen = UnitVolume(symbol: "cupsUSKitchen", converter: UnitConverterLinear(coefficient: 0.236588))

let myCups = Measurement(value: 1, unit: cupsUSKitchen)
let testOunces = myCups.converted(to: .fluidOunces)

Now, when I convert 1 cupUSKitchen into fluidOunces, it indeed returns 8 fl oz.


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