diff --git a/src/ObjLoading/StructuredDataDef/Parsing/Sequence/StructuredDataDefScopeSequences.cpp b/src/ObjLoading/StructuredDataDef/Parsing/Sequence/StructuredDataDefScopeSequences.cpp
index e532c204..a9a6c1e7 100644
--- a/src/ObjLoading/StructuredDataDef/Parsing/Sequence/StructuredDataDefScopeSequences.cpp
+++ b/src/ObjLoading/StructuredDataDef/Parsing/Sequence/StructuredDataDefScopeSequences.cpp
@@ -3,6 +3,7 @@
 #include <sstream>
 
 #include "Parsing/Simple/Matcher/SimpleMatcherFactory.h"
+#include "StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.h"
 
 namespace sdd::def_scope_sequences
 {
@@ -223,6 +224,18 @@ namespace sdd::def_scope_sequences
             }
         }
 
+        static void CalculateSizesAndOffsetsForDef(const StructuredDataDefParserState* state)
+        {
+            try
+            {
+                StructuredDataDefSizeCalculator::CalculateSizesAndOffsetsForDef(*state->m_current_def);
+            }
+            catch(SizeCalculationException& e)
+            {
+                throw ParsingException(TokenPos(), e.Message());
+            }
+        }
+
         static void SetDefSizeFromRootStruct(const StructuredDataDefParserState* state)
         {
             if (state->m_current_def->m_root_type.m_category == CommonStructuredDataTypeCategory::STRUCT
@@ -242,7 +255,7 @@ namespace sdd::def_scope_sequences
             CreateDefaultStructWhenNoStructsSpecified(state);
             EnsureAllUsedTypesHaveBeenDefined(state);
             ReplaceUndefinedTypeReference(state);
-            // TODO: Calculate struct sizes and property offsets
+            CalculateSizesAndOffsetsForDef(state);
             SetDefSizeFromRootStruct(state);
 
             if (!state->m_checksum_overriden)
diff --git a/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.cpp b/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.cpp
new file mode 100644
index 00000000..552849dd
--- /dev/null
+++ b/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.cpp
@@ -0,0 +1,143 @@
+#include "StructuredDataDefSizeCalculator.h"
+
+#include <cassert>
+#include <sstream>
+
+#include "Utils/ClassUtils.h"
+
+using namespace sdd;
+
+SizeCalculationException::SizeCalculationException(std::string message)
+    : m_message(std::move(message))
+{
+}
+
+const std::string& SizeCalculationException::Message() const
+{
+    return m_message;
+}
+
+char const* SizeCalculationException::what() const
+{
+    return m_message.c_str();
+}
+
+class StructuredDataDefSizeCalculatorInternal
+{
+    CommonStructuredDataDef& m_def;
+    std::vector<CommonStructuredDataType> m_type_stack;
+    std::vector<bool> m_struct_in_calculation;
+    std::vector<bool> m_struct_calculated;
+    std::vector<bool> m_indexed_array_calculated;
+    std::vector<bool> m_enumed_array_calculated;
+
+    _NORETURN void ThrowCircularDependencyException(const size_t structIndex) const
+    {
+        assert(structIndex < m_def.m_structs.size());
+
+        std::ostringstream ss;
+
+        ss << "Circular dependencies detected: ";
+
+        auto foundDependencyChainStart = false;
+        for(const auto& type : m_type_stack)
+        {
+            if(foundDependencyChainStart)
+            {
+                if(type.m_category == CommonStructuredDataTypeCategory::STRUCT)
+                {
+                    assert(type.m_info.type_index < m_def.m_structs.size());
+                    ss << " -> " << m_def.m_structs[type.m_info.type_index]->m_name;
+                }
+            }
+            else if (type.m_category == CommonStructuredDataTypeCategory::STRUCT && type.m_info.type_index == structIndex)
+            {
+                foundDependencyChainStart = true;
+                ss << m_def.m_structs[structIndex]->m_name;
+            }
+        }
+
+        ss << " -> " << m_def.m_structs[structIndex]->m_name;
+
+        throw SizeCalculationException(ss.str());
+    }
+
+    void CalculateForStruct(const size_t index, CommonStructuredDataStruct& _struct)
+    {
+        if (m_struct_calculated[index])
+            return;
+
+        if (m_struct_in_calculation[index])
+            ThrowCircularDependencyException(index);
+        m_struct_in_calculation[index] = true;
+
+        m_type_stack.emplace_back(CommonStructuredDataTypeCategory::STRUCT, index);
+
+        // TODO: Actually calculate stuff
+
+        m_struct_calculated[index] = true;
+        m_type_stack.pop_back();
+    }
+
+    void CalculateForIndexedArray(size_t index, CommonStructuredDataIndexedArray& indexedArray)
+    {
+        // TODO: Actually calculate stuff
+    }
+
+    void CalculateForEnumedArray(size_t index, CommonStructuredDataEnumedArray& enumedArray)
+    {
+        // TODO: Actually calculate stuff
+    }
+
+    void CalculateForType(const CommonStructuredDataType type)
+    {
+        switch (type.m_category)
+        {
+        case CommonStructuredDataTypeCategory::STRUCT:
+            assert(type.m_info.type_index < m_def.m_structs.size());
+            CalculateForStruct(type.m_info.type_index, *m_def.m_structs[type.m_info.type_index]);
+            break;
+        case CommonStructuredDataTypeCategory::INDEXED_ARRAY:
+            assert(type.m_info.type_index < m_def.m_indexed_arrays.size());
+            CalculateForIndexedArray(type.m_info.type_index, m_def.m_indexed_arrays[type.m_info.type_index]);
+            break;
+        case CommonStructuredDataTypeCategory::ENUM_ARRAY:
+            assert(type.m_info.type_index < m_def.m_enumed_arrays.size());
+            CalculateForEnumedArray(type.m_info.type_index, m_def.m_enumed_arrays[type.m_info.type_index]);
+            break;
+        default:
+            break;
+        }
+    }
+
+public:
+    explicit StructuredDataDefSizeCalculatorInternal(CommonStructuredDataDef& def)
+        : m_def(def),
+          m_struct_in_calculation(def.m_structs.size()),
+          m_struct_calculated(def.m_structs.size()),
+          m_indexed_array_calculated(def.m_indexed_arrays.size()),
+          m_enumed_array_calculated(def.m_enumed_arrays.size())
+    {
+    }
+
+    void CalculateSizesAndOffsets()
+    {
+        auto index = 0u;
+        for (auto& _struct : m_def.m_structs)
+            CalculateForStruct(index++, *_struct);
+
+        index = 0u;
+        for (auto& indexedArray : m_def.m_indexed_arrays)
+            CalculateForIndexedArray(index++, indexedArray);
+
+        index = 0u;
+        for (auto& enumedArray : m_def.m_enumed_arrays)
+            CalculateForEnumedArray(index++, enumedArray);
+    }
+};
+
+void StructuredDataDefSizeCalculator::CalculateSizesAndOffsetsForDef(CommonStructuredDataDef& def)
+{
+    StructuredDataDefSizeCalculatorInternal calculator(def);
+    calculator.CalculateSizesAndOffsets();
+}
diff --git a/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.h b/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.h
new file mode 100644
index 00000000..b3721cf8
--- /dev/null
+++ b/src/ObjLoading/StructuredDataDef/Parsing/StructuredDataDefSizeCalculator.h
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <string>
+#include <exception>
+
+#include "Utils/ClassUtils.h"
+#include "StructuredDataDef/CommonStructuredDataDef.h"
+
+namespace sdd
+{
+    class SizeCalculationException final : std::exception
+    {
+        std::string m_message;
+
+    public:
+        explicit SizeCalculationException(std::string message);
+
+        _NODISCARD const std::string& Message() const;
+        _NODISCARD char const* what() const override;
+    };
+
+    class StructuredDataDefSizeCalculator
+    {
+    public:
+        static void CalculateSizesAndOffsetsForDef(CommonStructuredDataDef& def);
+    };
+}
diff --git a/src/Utils/Utils/ClassUtils.h b/src/Utils/Utils/ClassUtils.h
index 4216d4a0..8fd50645 100644
--- a/src/Utils/Utils/ClassUtils.h
+++ b/src/Utils/Utils/ClassUtils.h
@@ -16,10 +16,16 @@
 #undef _NODISCARD
 #endif
 
+#ifdef _NORETURN
+#undef _NORETURN
+#endif
+
 #if _CPP_VERSION >= 201703L
 #define _NODISCARD [[nodiscard]]
+#define _NORETURN [[noreturn]]
 #else
 #define _NODISCARD
+#define _NORETURN
 #endif
 
 template <class T>