diff --git a/web/packages/new/photos/components/utils/thumbnail-grid-layout.ts b/web/packages/new/photos/components/utils/thumbnail-grid-layout.ts
new file mode 100644
index 0000000000..cfe1b9b34d
--- /dev/null
+++ b/web/packages/new/photos/components/utils/thumbnail-grid-layout.ts
@@ -0,0 +1,80 @@
+export interface ThumbnailGridLayoutParams {
+    /** The inline padding (px) of the thumbnail grid. */
+    paddingInline: number;
+    /** The number of columns in the thumbnail grid. */
+    columns: number;
+    /** The width (px) of each item. */
+    itemWidth: number;
+    /** The height (px) of each item. */
+    itemHeight: number;
+    /** The gap (px) between each grid item. */
+    gap: number;
+}
+
+/**
+ * Determine the layout parameters for a grid of thumbnails that would best fit
+ * the given width under various constraints.
+ *
+ * @param containerWidth The width available to the container. In our case,
+ * since the thumbnail grids span the entire available width, this is the width
+ * of the page itself.
+ */
+export const computeThumbnailGridLayoutParams = (
+    containerWidth: number,
+): ThumbnailGridLayoutParams => {
+    const paddingInline = getGapFromScreenEdge(containerWidth);
+    const fittableColumns = getFractionFittableColumns(containerWidth);
+
+    let columns = Math.floor(fittableColumns);
+    if (columns < MIN_COLUMNS) {
+        columns = MIN_COLUMNS;
+    }
+
+    const shrinkRatio = getShrinkRatio(containerWidth, columns);
+    const itemHeight = IMAGE_CONTAINER_MAX_HEIGHT * shrinkRatio;
+    const itemWidth = IMAGE_CONTAINER_MAX_WIDTH * shrinkRatio;
+    const gap = GAP_BTW_TILES;
+
+    return {
+        paddingInline,
+        columns,
+        itemWidth,
+        itemHeight,
+        gap,
+    };
+};
+
+/* TODO: Some of this code is also duplicated elsewhere. See if those places can
+   reuse the same function as above, with some extra params if needed.
+
+   So that the duplication is easier to identify, keeping the duplication
+   verbatim for now */
+
+const GAP_BTW_TILES = 4;
+const IMAGE_CONTAINER_MAX_HEIGHT = 180;
+const IMAGE_CONTAINER_MAX_WIDTH = 180;
+const MIN_COLUMNS = 4;
+
+function getFractionFittableColumns(width: number): number {
+    return (
+        (width - 2 * getGapFromScreenEdge(width) + GAP_BTW_TILES) /
+        (IMAGE_CONTAINER_MAX_WIDTH + GAP_BTW_TILES)
+    );
+}
+
+function getGapFromScreenEdge(width: number) {
+    if (width > MIN_COLUMNS * IMAGE_CONTAINER_MAX_WIDTH) {
+        return 24;
+    } else {
+        return 4;
+    }
+}
+
+function getShrinkRatio(width: number, columns: number) {
+    return (
+        (width -
+            2 * getGapFromScreenEdge(width) -
+            (columns - 1) * GAP_BTW_TILES) /
+        (columns * IMAGE_CONTAINER_MAX_WIDTH)
+    );
+}
diff --git a/web/packages/new/photos/pages/duplicates.tsx b/web/packages/new/photos/pages/duplicates.tsx
index e94b22247c..3f1c0140ae 100644
--- a/web/packages/new/photos/pages/duplicates.tsx
+++ b/web/packages/new/photos/pages/duplicates.tsx
@@ -440,6 +440,10 @@ const ListItem: React.FC<ListChildComponentProps<DuplicatesListProps>> = memo(
                     <Typography color={checked ? "text.base" : "text.muted"}>
                         {pt(`${count} items, ${itemSize} each`)}
                     </Typography>
+                    {/*
+                      The size of this Checkbox, 42px, drives the height of
+                      the header.
+                     */}
                     <Checkbox {...{ checked, onChange }} />
                 </Stack>
                 <ItemGrid>