diff --git a/hdyc-svelte/src/lib/components/Sidebar.svelte b/hdyc-svelte/src/lib/components/Sidebar.svelte
index 076cee1..10a3aa5 100644
--- a/hdyc-svelte/src/lib/components/Sidebar.svelte
+++ b/hdyc-svelte/src/lib/components/Sidebar.svelte
@@ -2,7 +2,7 @@
   import { browser } from '$app/environment';
   import { onMount } from 'svelte';
   import { page } from '$app/stores';
-  import { categories, getCalculatorsByCategory, type CalculatorDef } from '$lib/data/calculators';
+  import { categories, categoryOrder, getCalculatorsByCategory, type CalculatorDef } from '$lib/data/calculators';
 
   let expandedCategory = '';
   let expandedUnits: Record<string, string> = {};
@@ -31,34 +31,38 @@
     conversions: CalculatorDef[];
   };
 
-  $: categoryUnitGroups = Object.entries(categories).map(([key, meta]) => {
-    const buckets = new Map<string, UnitBucket>();
-    const calcs = getCalculatorsByCategory(key);
+  $: categoryUnitGroups = categoryOrder
+    .map(key => {
+      const meta = categories[key];
+      if (!meta) return null;
+      const buckets = new Map<string, UnitBucket>();
+      const calcs = getCalculatorsByCategory(key);
 
-    calcs.forEach(calc => {
-      [calc.labels.in1, calc.labels.in2].forEach(unit => {
-        const key = unit.toLowerCase();
-        const existing = buckets.get(key);
-        if (existing) {
-          existing.conversions.push(calc);
-        } else {
-          buckets.set(key, {
-            label: unit,
-            conversions: [calc],
-          });
-        }
+      calcs.forEach(calc => {
+        [calc.labels.in1, calc.labels.in2].forEach(unit => {
+          const lower = unit.toLowerCase();
+          const existing = buckets.get(lower);
+          if (existing) {
+            existing.conversions.push(calc);
+          } else {
+            buckets.set(lower, {
+              label: unit,
+              conversions: [calc],
+            });
+          }
+        });
       });
-    });
 
-    const units = [...buckets.entries()]
-      .sort(([a], [b]) => a.localeCompare(b))
-      .map(([, bucket]) => ({
-        label: bucket.label,
-        conversions: bucket.conversions.slice().sort((a, b) => a.name.localeCompare(b.name)),
-      }));
+      const units = [...buckets.entries()]
+        .sort(([a], [b]) => a.localeCompare(b))
+        .map(([, bucket]) => ({
+          label: bucket.label,
+          conversions: bucket.conversions.slice().sort((a, b) => a.name.localeCompare(b.name)),
+        }));
 
-    return { key, meta, units };
-  });
+      return { key, meta, units };
+    })
+    .filter(Boolean);
 
   function toggle(cat: string) {
     const wasOpen = expandedCategory === cat;
diff --git a/hdyc-svelte/src/lib/data/calculators.ts b/hdyc-svelte/src/lib/data/calculators.ts
index e9eb723..7474f77 100644
--- a/hdyc-svelte/src/lib/data/calculators.ts
+++ b/hdyc-svelte/src/lib/data/calculators.ts
@@ -39,6 +39,29 @@ export const categories: Record<string, { label: string; icon: string }> = {
   other:           { label: 'Other',               icon: '🔄' },
 };
 
+export const categoryOrder = [
+  'length',
+  'weight',
+  'temperature',
+  'volume',
+  'fluids',
+  'area',
+  'speed',
+  'pressure',
+  'energy',
+  'magnetism',
+  'power',
+  'data',
+  'time',
+  'angle',
+  'number-systems',
+  'radiation',
+  'electrical',
+  'force',
+  'light',
+  'other',
+] as const;
+
 export const calculators: CalculatorDef[] = [
   {"slug": "inches-to-feet", "name": "Inches to Feet", "category": "length", "type": "standard", "teaser": "If a shelf spans 36 inches, how many feet of trim does it cover?", "labels": {"in1": "Inches", "in2": "Feet"}, "factor": 12.0},
   {"slug": "kilograms-to-pounds", "name": "Kilograms to Pounds", "category": "weight", "type": "standard", "labels": {"in1": "Kilograms", "in2": "Pounds"}, "factor": 2.20462262},
@@ -1319,11 +1342,14 @@ export function getCalculatorsByCategory(category: string): CalculatorDef[] {
 }
 
 export function getCategoriesWithCounts(): { key: string; label: string; icon: string; count: number }[] {
-  return Object.entries(categories).map(([key, meta]) => ({
-    key,
-    ...meta,
-    count: calculators.filter(c => c.category === key && !c.hidden).length,
-  }));
+  return categoryOrder
+    .map(key => {
+      const meta = categories[key];
+      if (!meta) return null;
+      const count = calculators.filter(c => c.category === key && !c.hidden).length;
+      return { key, ...meta, count };
+    })
+    .filter(Boolean) as { key: string; label: string; icon: string; count: number }[];
 }
 
 export function searchCalculators(query: string): CalculatorDef[] {