diff --git a/pdnkit/LayerPanel.cpp b/pdnkit/LayerPanel.cpp
index f57e876..1bad1c0 100644
--- a/pdnkit/LayerPanel.cpp
+++ b/pdnkit/LayerPanel.cpp
@@ -1,6 +1,7 @@
 #include "LayerPanel.h"
 
 #include <QCheckBox>
+#include <QDoubleSpinBox>
 #include <QHBoxLayout>
 #include <QLabel>
 #include <QVBoxLayout>
@@ -71,13 +72,26 @@ void LayerPanel::setLayers(const std::vector<Entry>& layers) {
         name->setMinimumWidth(70);
         h->addWidget(name);
 
-        // Thickness label -- pulled from the LayerPanel Entry. Empty if the
-        // (setup (stackup ...)) block did not supply a value for this layer.
-        if (L.thickness_um > 0.0) {
-            auto* t = new QLabel(QString::number(L.thickness_um, 'f', 1) + " um");
+        // Thickness spinbox -- pre-loaded from the parsed stackup. Editing
+        // it propagates a thickness_changed() so MainWindow can override
+        // board_->stackup.layers[i].thickness in memory. Persisting back
+        // to the .kicad_pcb file needs an S-expr emitter -- separate work.
+        auto* t = new QDoubleSpinBox();
+        t->setRange(0.0, 1000.0);
+        t->setDecimals(2);
+        t->setSingleStep(1.0);
+        t->setSuffix(" um");
+        t->setValue(L.thickness_um);
+        t->setMaximumWidth(110);
+        if (L.thickness_um <= 0.0) {
             t->setStyleSheet("color: #888;");
-            h->addWidget(t);
+            t->setSpecialValueText("(unset)");
         }
+        connect(t, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
+                this, [this, ord](double v) {
+                    emit thickness_changed(ord, v * 1.0e-6);
+                });
+        h->addWidget(t);
         h->addStretch();
 
         rows_layout_->addWidget(row);
diff --git a/pdnkit/LayerPanel.h b/pdnkit/LayerPanel.h
index fdbe85b..ed14997 100644
--- a/pdnkit/LayerPanel.h
+++ b/pdnkit/LayerPanel.h
@@ -27,6 +27,12 @@ class LayerPanel : public QWidget {
 signals:
     void visibility_changed(int ordinal, bool visible);
 
+    // Emitted when the user edits a layer's thickness spinbox. The
+    // value is in meters (the panel does the um -> m conversion).
+    // MainWindow listens and writes board_->stackup.layers[i].thickness
+    // so the next analysis uses the override.
+    void thickness_changed(int ordinal, double thickness_m);
+
 private:
     void clearRows();
 
diff --git a/pdnkit/MainWindow.cpp b/pdnkit/MainWindow.cpp
index 8fada24..bfb9799 100644
--- a/pdnkit/MainWindow.cpp
+++ b/pdnkit/MainWindow.cpp
@@ -67,6 +67,22 @@ MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent) {
     dock->setWidget(layers_scroll);
     dock->setAllowedAreas(Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea);
     addDockWidget(Qt::RightDockWidgetArea, dock);
+    connect(layer_panel_, &LayerPanel::thickness_changed,
+            this, [this](int ord, double thickness_m) {
+                if (!board_) return;
+                for (auto& L : board_->stackup.layers) {
+                    if (L.ordinal == ord) {
+                        L.thickness = thickness_m;
+                        break;
+                    }
+                }
+                statusBar()->showMessage(
+                    QString("Layer %1 thickness updated to %2 um "
+                            "(in-memory, next analysis will use it)")
+                        .arg(ord)
+                        .arg(thickness_m * 1.0e6, 0, 'f', 1),
+                    6000);
+            });
     connect(layer_panel_, &LayerPanel::visibility_changed,
             canvas_, &PcbCanvas::setLayerVisibility);