diff --git a/src/ui/Picturarium.tsx b/src/ui/Picturarium.tsx
index 4c19d19..1ff0b83 100644
--- a/src/ui/Picturarium.tsx
+++ b/src/ui/Picturarium.tsx
@@ -10,6 +10,57 @@ import { Remote } from "../remote"
 //   I also like to keep views/states/messages/initialization/effects/update of one component in one single (even if giant) file (or a structure like `Component/...` + `Component.tsx`)
 // - Others school of thought are to grind all of these into fine dust and scatter the files all over the codebase (all state definitions in one giant folder, all messages/updates in another). I prefer not doing that. It violates locality too much for me, and I constantly have to jump between files "far-away".
 
+// === Config ===
+// prefered number of cols/rows. The page size (how many images are on a page) is calculated as `columns * rows`
+type Config = {
+  pageSize: number
+
+  mobileColumns: number
+  mobileRows: number
+
+  desktopColumns: number
+  desktopRows: number
+}
+
+const CONFIG = {
+  pageSize: 10,
+
+  mobileColumns: 2,
+  mobileRows: 5,
+
+  desktopColumns: 5,
+  desktopRows: 2,
+} as const satisfies Config
+// const CONFIG = {
+//   pageSize: 12,
+
+//   mobileColumns: 2,
+//   mobileRows: 6,
+
+//   desktopColumns: 4,
+//   desktopRows: 3,
+// } as const satisfies Config
+
+// Could do comptime assert: `size = mobile product`, and `size = desktop product`, but this is pretty heavy in TS.
+assertValidConfig(CONFIG)
+
+function assertValidConfig(config: Config): void {
+  const mobilePageSize = config.mobileColumns * config.mobileRows
+  const desktopPageSize = config.desktopColumns * config.desktopRows
+
+  if (mobilePageSize !== config.pageSize) {
+    throw new Error(
+      `Invalid config: mobile grid defines ${String(mobilePageSize)} images, but pageSize is ${String(config.pageSize)}`,
+    )
+  }
+
+  if (desktopPageSize !== config.pageSize) {
+    throw new Error(
+      `Invalid config: desktop grid defines ${String(desktopPageSize)} images, but pageSize is ${String(config.pageSize)}`,
+    )
+  }
+}
+
 // === Image ===
 type ImageId = string
 type ImageRef = string
@@ -28,45 +79,44 @@ const Dimension = {
 }
 
 // === Page ===
-type PageNumber = number
+type PageIndex = number
 
 type Page = {
-  page: PageNumber
-  limit: number // page size
+  index: PageIndex
+  size: number
 }
 type PageKey = string
 
-const LIMIT = 10
-const FIRST_PAGE: PageNumber = 1
+const FIRST_PAGE: PageIndex = 1
 
 const Page = {
   init(): Page {
-    return { page: FIRST_PAGE, limit: LIMIT }
+    return { index: FIRST_PAGE, size: CONFIG.pageSize }
   },
   next(page: Page): Page {
-    return { ...page, page: page.page + 1 }
+    return { ...page, index: page.index + 1 }
   },
   previous(page: Page): Page {
     // Could do
     // if (page.page == FIRST_PAGE) { return page }
     // this preserves identity of object, so is nicer for `useEffect`, but it's waaaay to subtle. So I'm not relying on that.
-    return { ...page, page: Math.max(FIRST_PAGE, page.page - 1) }
+    return { ...page, index: Math.max(FIRST_PAGE, page.index - 1) }
   },
   eq(page0: Page, page1: Page): boolean {
-    return page0.page === page1.page && page0.limit === page1.limit
+    return page0.index === page1.index && page0.size === page1.size
   },
   // for hashing in maps to avoid identity problems
   key(page: Page): PageKey {
-    return `${String(page.page)}:${String(page.limit)}`
+    return `${String(page.index)}:${String(page.size)}`
   },
   isFirst(page: Page): boolean {
-    return page.page === FIRST_PAGE
+    return page.index === FIRST_PAGE
   },
 }
 
 // === api ===
 async function getImageIds(page: Page): Promise<Result<ImageId[], RequestError>> {
-  const result = await getPicsumImages(page)
+  const result = await getPicsumImages({ page: page.index, limit: page.size })
   return Result.map(result, (data) => data.map(({ id }) => id))
 }
 
@@ -233,8 +283,8 @@ function imageGridStyle(dimension: Dimension) {
   return {
     display: "grid",
     gridTemplateColumns: {
-      xs: `repeat(2, ${String(dimension.width)}px)`,
-      md: `repeat(5, ${String(dimension.width)}px)`,
+      xs: `repeat(${String(CONFIG.mobileColumns)}, ${String(dimension.width)}px)`,
+      md: `repeat(${String(CONFIG.desktopColumns)}, ${String(dimension.width)}px)`,
     },
     gridAutoRows: `${String(dimension.height)}px`,
     gap: 2,
@@ -243,7 +293,7 @@ function imageGridStyle(dimension: Dimension) {
 
 // 2x5 on mobile, 5x2 on desktop (assuming 10 images per page)
 function ImagesSkeleton({ visible = true }: { visible?: boolean }) {
-  const images = Array.from({ length: 10 })
+  const images = Array.from({ length: CONFIG.pageSize })
   return (
     <Box sx={imageGridStyle(Dimension.medium)}>
       {images.map((_, index) =>
@@ -396,7 +446,7 @@ export default function Picturarium() {
               color: "oklch(65% 0.02 260)",
             }}
           >
-            {state.page.page}
+            {state.page.index}
           </Typography>
           <Button
             onClick={() => {