Here's my solution for the challenge. I used volume units and created an enum that integrates Measurement to handle the conversion automatically.

import SwiftUI

struct ContentView: View {
    @State private var conversionValue = 0.0
    @FocusState private var valueIsFocused: Bool
    @State private var inputUnit = ConversionUnits.L
    @State private var outputUnit = ConversionUnits.gal

    private enum ConversionUnits: String, CaseIterable {
        case mL
        case L
        case cup
        case pt
        case gal

        var unit: UnitVolume {
            switch self {
            case .mL: return UnitVolume.milliliters
            case .L: return UnitVolume.liters
            case .cup: return UnitVolume.cups
            case .pt: return UnitVolume.pints
            case .gal: return UnitVolume.gallons
            }
        }
    }

    private var convertedValue: Double {
        let inValue = Measurement(value: conversionValue, unit: inputUnit.unit)
        let value = inValue.converted(to: outputUnit.unit)

        return value.value
    }

    var body: some View {
        NavigationStack {
            Form {
                Section {
                    TextField("Value to convert", value: $conversionValue, format: .number)
                        .keyboardType(.decimalPad)
                        .focused($valueIsFocused)
                } header: {
                    Text("Value to convert")
                }

                Section {
                    Picker("Source Unit", selection: $inputUnit) {
                        ForEach(ConversionUnits.allCases, id: \.self) {
                            Text($0.rawValue)
                        }
                    }
                    .pickerStyle(.segmented)
                } header: {
                    Text("Convert from")
                }

                Section {
                    Picker("Source Unit", selection: $outputUnit) {
                        ForEach(ConversionUnits.allCases, id: \.self) {
                            Text($0.rawValue)
                        }
                    }
                    .pickerStyle(.segmented)
                } header: {
                    Text("Convert to")
                }

                Section {
                    Text(convertedValue.formatted())
                } header: {
                    Text("Converted value")
                }
            }
            .navigationTitle("Unit Conversion")
            .toolbar {
                ToolbarItemGroup(placement: .keyboard) {
                    Spacer()

                    Button("Done") {
                        valueIsFocused = false
                    }
                }
            }
        }
    }
}