diff --git a/layout/generic/nsGridContainerFrame.cpp b/layout/generic/nsGridContainerFrame.cpp
index fdd33f9e5669..89e6d9a0c031 100644
--- a/layout/generic/nsGridContainerFrame.cpp
+++ b/layout/generic/nsGridContainerFrame.cpp
@@ -14,9 +14,11 @@
 #include "nsHashKeys.h"
 #include "nsPresContext.h"
 #include "nsReadableUtils.h"
+#include "nsRuleNode.h"
 #include "nsStyleContext.h"
 
 using namespace mozilla;
+typedef nsGridContainerFrame::TrackSize TrackSize;
 
 /**
  * Search for the aNth occurrence of aName in aNameList (forward), starting at
@@ -687,6 +689,85 @@ nsGridContainerFrame::PlaceGridItems(const nsStylePosition* aStyle)
   }
 }
 
+static void
+InitializeTrackSize(nscoord aPercentageBasis,
+                    const nsStyleCoord& aMinCoord,
+                    const nsStyleCoord& aMaxCoord,
+                    TrackSize* aTrackSize)
+{
+  // http://dev.w3.org/csswg/css-grid/#algo-init
+  nscoord& base = aTrackSize->mBase;
+  switch (aMaxCoord.GetUnit()) {
+    case eStyleUnit_Enumerated:
+    case eStyleUnit_FlexFraction:
+      base = 0;
+      break;
+    default:
+      base = nsRuleNode::ComputeCoordPercentCalc(aMinCoord, aPercentageBasis);
+  }
+  nscoord& limit = aTrackSize->mLimit;
+  switch (aMaxCoord.GetUnit()) {
+    case eStyleUnit_Enumerated:
+      limit = NS_UNCONSTRAINEDSIZE;
+      break;
+    case eStyleUnit_FlexFraction:
+      limit = base;
+      break;
+    default:
+      limit = nsRuleNode::ComputeCoordPercentCalc(aMaxCoord, aPercentageBasis);
+      if (limit < base) {
+        limit = base;
+      }
+  }
+}
+
+static void
+InitializeTrackSizes(nscoord aPercentageBasis,
+                     const nsTArray<nsStyleCoord>& aMinSizingFunctions,
+                     const nsTArray<nsStyleCoord>& aMaxSizingFunctions,
+                     const nsStyleCoord& aAutoMinFunction,
+                     const nsStyleCoord& aAutoMaxFunction,
+                     nsTArray<TrackSize>& aResults)
+{
+  MOZ_ASSERT(aResults.Length() >= aMinSizingFunctions.Length());
+  MOZ_ASSERT(aMinSizingFunctions.Length() == aMaxSizingFunctions.Length());
+  const size_t len = aMinSizingFunctions.Length();
+  size_t i = 0;
+  for (; i < len; ++i) {
+    InitializeTrackSize(aPercentageBasis,
+                        aMinSizingFunctions[i], aMinSizingFunctions[i],
+                        &aResults[i]);
+  }
+  for (; i < aResults.Length(); ++i) {
+    InitializeTrackSize(aPercentageBasis,
+                        aAutoMinFunction, aAutoMaxFunction,
+                        &aResults[i]);
+  }
+}
+
+void
+nsGridContainerFrame::CalculateTrackSizes(const LogicalSize& aPercentageBasis,
+                                          const nsStylePosition* aStyle,
+                                          nsTArray<TrackSize>& aColSizes,
+                                          nsTArray<TrackSize>& aRowSizes)
+{
+  aColSizes.SetLength(mGridColEnd - 1);
+  aRowSizes.SetLength(mGridRowEnd - 1);
+  WritingMode wm = GetWritingMode();
+  InitializeTrackSizes(aPercentageBasis.ISize(wm),
+                       aStyle->mGridTemplateColumns.mMinTrackSizingFunctions,
+                       aStyle->mGridTemplateColumns.mMaxTrackSizingFunctions,
+                       aStyle->mGridAutoColumnsMin,
+                       aStyle->mGridAutoColumnsMax,
+                       aColSizes);
+  InitializeTrackSizes(aPercentageBasis.BSize(wm),
+                       aStyle->mGridTemplateRows.mMinTrackSizingFunctions,
+                       aStyle->mGridTemplateRows.mMaxTrackSizingFunctions,
+                       aStyle->mGridAutoRowsMin,
+                       aStyle->mGridAutoRowsMax,
+                       aRowSizes);
+}
+
 void
 nsGridContainerFrame::Reflow(nsPresContext*           aPresContext,
                              nsHTMLReflowMetrics&     aDesiredSize,
@@ -721,6 +802,11 @@ nsGridContainerFrame::Reflow(nsPresContext*           aPresContext,
   InitImplicitNamedAreas(stylePos);
   PlaceGridItems(stylePos);
 
+  nsAutoTArray<TrackSize, 32> colSizes;
+  nsAutoTArray<TrackSize, 32> rowSizes;
+  LogicalSize percentageBasis(wm, aReflowState.ComputedISize(), contentBSize);
+  CalculateTrackSizes(percentageBasis, stylePos, colSizes, rowSizes);
+
   aStatus = NS_FRAME_COMPLETE;
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize);
 }
diff --git a/layout/generic/nsGridContainerFrame.h b/layout/generic/nsGridContainerFrame.h
index 59deb0e9519e..e3e0565751cd 100644
--- a/layout/generic/nsGridContainerFrame.h
+++ b/layout/generic/nsGridContainerFrame.h
@@ -38,6 +38,11 @@ public:
   virtual nsresult GetFrameName(nsAString& aResult) const MOZ_OVERRIDE;
 #endif
 
+  struct TrackSize {
+    nscoord mBase;
+    nscoord mLimit;
+  };
+
 protected:
   typedef mozilla::css::GridNamedArea GridNamedArea;
   friend nsContainerFrame* NS_NewGridContainerFrame(nsIPresShell* aPresShell,
@@ -258,6 +263,14 @@ protected:
     mGridRowEnd = std::max(mGridRowEnd, aArea.mRows.HypotheticalEnd());
   }
 
+  /**
+   * Calculate track sizes.
+   */
+  void CalculateTrackSizes(const mozilla::LogicalSize& aPercentageBasis,
+                           const nsStylePosition*      aStyle,
+                           nsTArray<TrackSize>&        aColSizes,
+                           nsTArray<TrackSize>&        aRowSizes);
+
   /**
    * Helper method for ResolveLineRange.
    * @see ResolveLineRange