diff --git a/OpenNest.Core/Shapes/PipeSizes.cs b/OpenNest.Core/Shapes/PipeSizes.cs
new file mode 100644
index 0000000..d577a3a
--- /dev/null
+++ b/OpenNest.Core/Shapes/PipeSizes.cs
@@ -0,0 +1,69 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest.Shapes
+{
+    public static class PipeSizes
+    {
+        public readonly record struct Entry(string Label, double OuterDiameter);
+
+        public static IReadOnlyList<Entry> All { get; } = new List<Entry>
+        {
+            new Entry("1/8",    0.405),
+            new Entry("1/4",    0.540),
+            new Entry("3/8",    0.675),
+            new Entry("1/2",    0.840),
+            new Entry("3/4",    1.050),
+            new Entry("1",      1.315),
+            new Entry("1 1/4",  1.660),
+            new Entry("1 1/2",  1.900),
+            new Entry("2",      2.375),
+            new Entry("2 1/2",  2.875),
+            new Entry("3",      3.500),
+            new Entry("3 1/2",  4.000),
+            new Entry("4",      4.500),
+            new Entry("4 1/2",  5.000),
+            new Entry("5",      5.563),
+            new Entry("6",      6.625),
+            new Entry("7",      7.625),
+            new Entry("8",      8.625),
+            new Entry("9",      9.625),
+            new Entry("10",    10.750),
+            new Entry("11",    11.750),
+            new Entry("12",    12.750),
+            new Entry("14",    14.000),
+            new Entry("16",    16.000),
+            new Entry("18",    18.000),
+            new Entry("20",    20.000),
+            new Entry("24",    24.000),
+            new Entry("26",    26.000),
+            new Entry("28",    28.000),
+            new Entry("30",    30.000),
+            new Entry("32",    32.000),
+            new Entry("34",    34.000),
+            new Entry("36",    36.000),
+            new Entry("42",    42.000),
+            new Entry("48",    48.000),
+        };
+
+        public static bool TryGetOD(string label, out double outerDiameter)
+        {
+            foreach (var entry in All)
+            {
+                if (entry.Label == label)
+                {
+                    outerDiameter = entry.OuterDiameter;
+                    return true;
+                }
+            }
+
+            outerDiameter = 0;
+            return false;
+        }
+
+        public static IEnumerable<Entry> GetFittingSizes(double maxOD)
+        {
+            return All.Where(e => e.OuterDiameter <= maxOD);
+        }
+    }
+}
diff --git a/OpenNest.Tests/Shapes/PipeSizesTests.cs b/OpenNest.Tests/Shapes/PipeSizesTests.cs
new file mode 100644
index 0000000..bb588cd
--- /dev/null
+++ b/OpenNest.Tests/Shapes/PipeSizesTests.cs
@@ -0,0 +1,54 @@
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.Shapes;
+
+public class PipeSizesTests
+{
+    [Fact]
+    public void All_ContainsExpectedCount()
+    {
+        Assert.Equal(35, PipeSizes.All.Count);
+    }
+
+    [Fact]
+    public void All_IsSortedByOuterDiameterAscending()
+    {
+        for (var i = 1; i < PipeSizes.All.Count; i++)
+            Assert.True(PipeSizes.All[i].OuterDiameter > PipeSizes.All[i - 1].OuterDiameter);
+    }
+
+    [Theory]
+    [InlineData("1/8", 0.405)]
+    [InlineData("1/2", 0.840)]
+    [InlineData("2", 2.375)]
+    [InlineData("2 1/2", 2.875)]
+    [InlineData("12", 12.750)]
+    [InlineData("48", 48.000)]
+    public void TryGetOD_KnownLabel_ReturnsExpectedOD(string label, double expected)
+    {
+        Assert.True(PipeSizes.TryGetOD(label, out var od));
+        Assert.Equal(expected, od, 0.001);
+    }
+
+    [Fact]
+    public void TryGetOD_UnknownLabel_ReturnsFalse()
+    {
+        Assert.False(PipeSizes.TryGetOD("bogus", out _));
+    }
+
+    [Fact]
+    public void GetFittingSizes_FiltersByMaxOD()
+    {
+        var results = PipeSizes.GetFittingSizes(3.0).ToList();
+
+        Assert.Contains(results, e => e.Label == "2 1/2");
+        Assert.DoesNotContain(results, e => e.Label == "3");
+        Assert.DoesNotContain(results, e => e.Label == "4");
+    }
+
+    [Fact]
+    public void GetFittingSizes_MaxSmallerThanSmallest_ReturnsEmpty()
+    {
+        Assert.Empty(PipeSizes.GetFittingSizes(0.1));
+    }
+}