Added imperial area units and unit tests for them:

SquareMiles, SquareYards, SquareFeet, SquareInches.

Author: angularsen

Src/UnitsNet/Area.cs

@@ -8,6 +8,10 @@ public struct Area : IComparable, IComparable<Area>
         private const double SquareDecimetersToSquareMetersRatio = 1E-2;
         private const double SquareCentimetersToSquareMetersRatio = 1E-4;
         private const double SquareMillimetersToSquareMetersRatio = 1E-6;
+        private const double SquareMilesToSquareMetersRatio = 2.59*1E+6;
+        private const double SquareYardsToSquareMetersRatio = 0.836127;
+        private const double SquareFeetToSquareMetersRatio = 0.092903;
+        private const double SquareInchesToSquareMetersRatio = 0.00064516;
 
         public readonly double SquareMeters;
 
@@ -38,6 +42,27 @@ public double SquareMillimeters
             get { return SquareMeters / SquareMillimetersToSquareMetersRatio; }
         }
 
+        public double SquareMiles
+        {
+            get { return SquareMeters / SquareMilesToSquareMetersRatio; }
+        }
+
+        public double SquareYards
+        {
+            get { return SquareMeters / SquareYardsToSquareMetersRatio; }
+        }
+
+        public double SquareFeet
+        {
+            get { return SquareMeters / SquareFeetToSquareMetersRatio; }
+        }
+
+        public double SquareInches
+        {
+            get { return SquareMeters / SquareInchesToSquareMetersRatio; }
+        }
+
+
         #endregion
 
         #region Static
@@ -88,6 +113,26 @@ public static Area FromSquareMillimeters(double squareMillimeters)
             return new Area(squareMillimeters * SquareMillimetersToSquareMetersRatio);
         }
 
+        public static Area FromSquareMiles(double sqmi)
+        {
+            return new Area(sqmi * SquareMilesToSquareMetersRatio);
+        }
+
+        public static Area FromSquareYards(double yds)
+        {
+            return new Area(yds * SquareYardsToSquareMetersRatio);
+        }
+
+        public static Area FromSquareFeet(double ft)
+        {
+            return new Area(ft * SquareFeetToSquareMetersRatio);
+        }
+
+        public static Area FromSquareInches(double inches)
+        {
+            return new Area(inches * SquareInchesToSquareMetersRatio);
+        }
+
         #endregion
 
         #region Arithmetic operators

Src/UnitsNet/Unit.cs

@@ -97,6 +97,12 @@ public enum Unit
         SquareCentimeter,
         SquareMillimeter,
 
+	// Area Imperial
+        SquareMile,
+        SquareYard,
+        SquareFoot,
+        SquareInch,
+
         // Volume
         CubicKilometer,
         CubicMeter,

Src/UnitsNet/UnitConverter.cs

@@ -229,6 +229,15 @@ private static bool TryConvertArea(double value, Unit fromUnit, Unit toUnit, out
                 case Unit.SquareMillimeter:
                     return TryConvert(Area.FromSquareMillimeters(value), toUnit, out newValue);
 
+                case Unit.SquareMile:
+                    return TryConvert(Area.FromSquareMiles(value), toUnit, out newValue);
+                case Unit.SquareYard:
+                    return TryConvert(Area.FromSquareYards(value), toUnit, out newValue);
+                case Unit.SquareFoot:
+                    return TryConvert(Area.FromSquareFeet(value), toUnit, out newValue);
+                case Unit.SquareInch:
+                    return TryConvert(Area.FromSquareInches(value), toUnit, out newValue);
+
                 default:
                     newValue = 0;
                     return false;
@@ -368,6 +377,19 @@ private static bool TryConvert(Area volume, Unit toUnit, out double newValue)
                     newValue = volume.SquareMillimeters;
                     return true;
 
+                case Unit.SquareMile:
+                    newValue = volume.SquareMiles;
+                    return true;
+                case Unit.SquareYard:
+                    newValue = volume.SquareYards;
+                    return true;
+                case Unit.SquareFoot:
+                    newValue = volume.SquareFeet;
+                    return true;
+                case Unit.SquareInch:
+                    newValue = volume.SquareInches;
+                    return true;
+
                 default:
                     newValue = 0;
                     return false;

Tests/AreaTests.cs

@@ -17,6 +17,11 @@ public void SquareMetersToAreaUnits()
             Assert.AreEqual(1E2, _squareMeter.SquareDecimeters, Delta);
             Assert.AreEqual(1E4, _squareMeter.SquareCentimeters, Delta);
             Assert.AreEqual(1E6, _squareMeter.SquareMillimeters, Delta);
+
+            Assert.AreEqual(3.86102*1E-7, _squareMeter.SquareMiles, Delta);
+            Assert.AreEqual(1.19599, _squareMeter.SquareYards, Delta);
+            Assert.AreEqual(10.76391, _squareMeter.SquareFeet, Delta);
+            Assert.AreEqual(1550.003100, _squareMeter.SquareInches, Delta);
         }
 
         [Test]
@@ -27,6 +32,11 @@ public void AreaUnitsRoundTrip()
             Assert.AreEqual(1, Area.FromSquareDecimeters(_squareMeter.SquareDecimeters).SquareMeters, Delta);
             Assert.AreEqual(1, Area.FromSquareCentimeters(_squareMeter.SquareCentimeters).SquareMeters, Delta);
             Assert.AreEqual(1, Area.FromSquareMillimeters(_squareMeter.SquareMillimeters).SquareMeters, Delta);
+
+            Assert.AreEqual(1, Area.FromSquareMiles(_squareMeter.SquareMiles).SquareMeters, Delta);
+            Assert.AreEqual(1, Area.FromSquareYards(_squareMeter.SquareYards).SquareMeters, Delta);
+            Assert.AreEqual(1, Area.FromSquareFeet(_squareMeter.SquareFeet).SquareMeters, Delta);
+            Assert.AreEqual(1, Area.FromSquareInches(_squareMeter.SquareInches).SquareMeters, Delta);
         }
 
         [Test]