diff --git a/renderdoc/driver/d3d11/d3d11_postvs.cpp b/renderdoc/driver/d3d11/d3d11_postvs.cpp
index bd618ccb6..f523db932 100644
--- a/renderdoc/driver/d3d11/d3d11_postvs.cpp
+++ b/renderdoc/driver/d3d11/d3d11_postvs.cpp
@@ -324,8 +324,7 @@ void D3D11Replay::InitPostVSBuffers(uint32_t eventId)
       if(m_SOBufferSize < outputSize)
       {
         uint64_t oldSize = m_SOBufferSize;
-        while(m_SOBufferSize < outputSize)
-          m_SOBufferSize *= 2;
+        m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
         RDCWARN("Resizing stream-out buffer from %llu to %llu", oldSize, m_SOBufferSize);
         CreateSOBuffers();
 
@@ -439,8 +438,7 @@ void D3D11Replay::InitPostVSBuffers(uint32_t eventId)
       if(m_SOBufferSize < outputSize)
       {
         uint64_t oldSize = m_SOBufferSize;
-        while(m_SOBufferSize < outputSize)
-          m_SOBufferSize *= 2;
+        m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
         RDCWARN("Resizing stream-out buffer from %llu to %llu", oldSize, m_SOBufferSize);
         CreateSOBuffers();
         if(!m_SOStagingBuffer)
@@ -777,11 +775,12 @@ void D3D11Replay::InitPostVSBuffers(uint32_t eventId)
                                           sizeof(D3D11_QUERY_DATA_SO_STATISTICS), 0);
       } while(hr == S_FALSE);
 
-      if(m_SOBufferSize < stride * numPrims.PrimitivesStorageNeeded * 3)
+      uint64_t outputSize = stride * numPrims.PrimitivesStorageNeeded * 3;
+
+      if(m_SOBufferSize < outputSize)
       {
         uint64_t oldSize = m_SOBufferSize;
-        while(m_SOBufferSize < stride * numPrims.PrimitivesStorageNeeded * 3)
-          m_SOBufferSize *= 2;
+        m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
         RDCWARN("Resizing stream-out buffer from %llu to %llu", oldSize, m_SOBufferSize);
         CreateSOBuffers();
         if(!m_SOStagingBuffer)
@@ -900,7 +899,7 @@ void D3D11Replay::InitPostVSBuffers(uint32_t eventId)
         (uint32_t)bytesWritten, D3D11_USAGE_IMMUTABLE, D3D11_BIND_VERTEX_BUFFER, 0, 0, 0,
     };
 
-    if(bytesWritten >= m_SOBufferSize)
+    if(bytesWritten > m_SOBufferSize)
     {
       RDCERR("Generated output data too large: %08x", bufferDesc.ByteWidth);
 
diff --git a/renderdoc/driver/d3d12/d3d12_postvs.cpp b/renderdoc/driver/d3d12/d3d12_postvs.cpp
index afd60cd5f..092114eb4 100644
--- a/renderdoc/driver/d3d12/d3d12_postvs.cpp
+++ b/renderdoc/driver/d3d12/d3d12_postvs.cpp
@@ -329,8 +329,7 @@ void D3D12Replay::InitPostVSBuffers(uint32_t eventId)
     if(m_SOBufferSize < outputSize)
     {
       uint64_t oldSize = m_SOBufferSize;
-      while(m_SOBufferSize < outputSize)
-        m_SOBufferSize *= 2;
+      m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
       RDCWARN("Resizing stream-out buffer from %llu to %llu for output data", oldSize,
               m_SOBufferSize);
       recreate = true;
@@ -434,11 +433,12 @@ void D3D12Replay::InitPostVSBuffers(uint32_t eventId)
         indexRemap[indices[i]] = i;
       }
 
-      if(m_SOBufferSize / sizeof(Vec4f) < indices.size() * sizeof(uint32_t))
+      outputSize = uint64_t(indices.size() * sizeof(uint32_t) * sizeof(Vec4f));
+
+      if(m_SOBufferSize < outputSize)
       {
         uint64_t oldSize = m_SOBufferSize;
-        while(m_SOBufferSize / sizeof(Vec4f) < indices.size() * sizeof(uint32_t))
-          m_SOBufferSize *= 2;
+        m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
         RDCWARN("Resizing stream-out buffer from %llu to %llu for indices", oldSize, m_SOBufferSize);
         recreate = true;
       }
@@ -886,11 +886,12 @@ void D3D12Replay::InitPostVSBuffers(uint32_t eventId)
       range.End = 0;
       m_SOStagingBuffer->Unmap(0, &range);
 
-      if(m_SOBufferSize < data->PrimitivesStorageNeeded * 3 * stride)
+      uint64_t outputSize = data->PrimitivesStorageNeeded * 3 * stride;
+
+      if(m_SOBufferSize < outputSize)
       {
         uint64_t oldSize = m_SOBufferSize;
-        while(m_SOBufferSize < data->PrimitivesStorageNeeded * 3 * stride)
-          m_SOBufferSize *= 2;
+        m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
         RDCWARN("Resizing stream-out buffer from %llu to %llu for output", oldSize, m_SOBufferSize);
         CreateSOBuffers();
       }
@@ -1025,11 +1026,12 @@ void D3D12Replay::InitPostVSBuffers(uint32_t eventId)
         D3D12_QUERY_DATA_SO_STATISTICS *data;
         hr = m_SOStagingBuffer->Map(0, &range, (void **)&data);
 
-        if(m_SOBufferSize < data->PrimitivesStorageNeeded * 3 * stride)
+        uint64_t outputSize = data->PrimitivesStorageNeeded * 3 * stride;
+
+        if(m_SOBufferSize < outputSize)
         {
           uint64_t oldSize = m_SOBufferSize;
-          while(m_SOBufferSize < data->PrimitivesStorageNeeded * 3 * stride)
-            m_SOBufferSize *= 2;
+          m_SOBufferSize = CalcMeshOutputSize(m_SOBufferSize, outputSize);
           RDCWARN("Resizing stream-out buffer from %llu to %llu for output", oldSize, m_SOBufferSize);
           CreateSOBuffers();
 
diff --git a/renderdoc/driver/gl/gl_postvs.cpp b/renderdoc/driver/gl/gl_postvs.cpp
index f5eb8435f..5783b2002 100644
--- a/renderdoc/driver/gl/gl_postvs.cpp
+++ b/renderdoc/driver/gl/gl_postvs.cpp
@@ -375,8 +375,7 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
     if(DebugData.feedbackBufferSize < outputSize)
     {
       uint64_t oldSize = DebugData.feedbackBufferSize;
-      while(DebugData.feedbackBufferSize < outputSize)
-        DebugData.feedbackBufferSize *= 2;
+      DebugData.feedbackBufferSize = CalcMeshOutputSize(DebugData.feedbackBufferSize, outputSize);
       RDCWARN("Resizing xfb buffer from %llu to %llu for output", oldSize,
               DebugData.feedbackBufferSize);
       if(DebugData.feedbackBufferSize > INTPTR_MAX)
@@ -495,8 +494,7 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
     if(DebugData.feedbackBufferSize < outputSize)
     {
       uint64_t oldSize = DebugData.feedbackBufferSize;
-      while(DebugData.feedbackBufferSize < outputSize)
-        DebugData.feedbackBufferSize *= 2;
+      DebugData.feedbackBufferSize = CalcMeshOutputSize(DebugData.feedbackBufferSize, outputSize);
       RDCWARN("Resizing xfb buffer from %llu to %llu for output", oldSize,
               DebugData.feedbackBufferSize);
       if(DebugData.feedbackBufferSize > INTPTR_MAX)
@@ -1051,8 +1049,8 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
       if(DebugData.feedbackBufferSize < maxOutputSize)
       {
         uint64_t oldSize = DebugData.feedbackBufferSize;
-        while(DebugData.feedbackBufferSize < maxOutputSize)
-          DebugData.feedbackBufferSize *= 2;
+        DebugData.feedbackBufferSize =
+            CalcMeshOutputSize(DebugData.feedbackBufferSize, maxOutputSize);
         RDCWARN("Conservatively resizing xfb buffer from %llu to %llu for output", oldSize,
                 DebugData.feedbackBufferSize);
         if(DebugData.feedbackBufferSize > INTPTR_MAX)
diff --git a/renderdoc/replay/replay_driver.cpp b/renderdoc/replay/replay_driver.cpp
index 986020782..cb31df4a3 100644
--- a/renderdoc/replay/replay_driver.cpp
+++ b/renderdoc/replay/replay_driver.cpp
@@ -207,6 +207,20 @@ void PatchLineStripIndexBuffer(const DrawcallDescription *draw, uint8_t *idx8, u
 #undef IDX_VALUE
 }
 
+uint64_t CalcMeshOutputSize(uint64_t curSize, uint64_t requiredOutput)
+{
+  // resize exponentially up to 256MB to avoid repeated resizes
+  while(curSize < requiredOutput && curSize < 0x10000000ULL)
+    curSize *= 2;
+
+  // after that, just align the required size up to 16MB and allocate that. Otherwise we can
+  // vastly-overallocate at large sizes.
+  if(curSize < requiredOutput)
+    curSize = AlignUp(requiredOutput, 0x1000000ULL);
+
+  return curSize;
+}
+
 FloatVector HighlightCache::InterpretVertex(const byte *data, uint32_t vert, const MeshDisplay &cfg,
                                             const byte *end, bool useidx, bool &valid)
 {
diff --git a/renderdoc/replay/replay_driver.h b/renderdoc/replay/replay_driver.h
index 08e1f883d..f596f21c5 100644
--- a/renderdoc/replay/replay_driver.h
+++ b/renderdoc/replay/replay_driver.h
@@ -236,6 +236,8 @@ DrawcallDescription *SetupDrawcallPointers(std::vector<DrawcallDescription *> &d
 void PatchLineStripIndexBuffer(const DrawcallDescription *draw, uint8_t *idx8, uint16_t *idx16,
                                uint32_t *idx32, std::vector<uint32_t> &patchedIndices);
 
+uint64_t CalcMeshOutputSize(uint64_t curSize, uint64_t requiredOutput);
+
 // simple cache for when we need buffer data for highlighting
 // vertices, typical use will be lots of vertices in the same
 // mesh, not jumping back and forth much between meshes.