diff --git a/src/lib/server/unit-consolidation.ts b/src/lib/server/unit-consolidation.ts
new file mode 100644
index 0000000..ce22f28
--- /dev/null
+++ b/src/lib/server/unit-consolidation.ts
@@ -0,0 +1,11 @@
+export type UnitFamily = 'weight' | 'volume' | string;
+
+const WEIGHT_UNITS = new Set(['g', 'kg']);
+const VOLUME_UNITS = new Set(['ml', 'l']);
+
+export function unitFamily(unit: string | null | undefined): UnitFamily {
+  const u = (unit ?? '').trim().toLowerCase();
+  if (WEIGHT_UNITS.has(u)) return 'weight';
+  if (VOLUME_UNITS.has(u)) return 'volume';
+  return u;
+}
diff --git a/tests/unit/unit-consolidation.test.ts b/tests/unit/unit-consolidation.test.ts
new file mode 100644
index 0000000..40b6cb5
--- /dev/null
+++ b/tests/unit/unit-consolidation.test.ts
@@ -0,0 +1,28 @@
+import { describe, it, expect } from 'vitest';
+import { unitFamily } from '../../src/lib/server/unit-consolidation';
+
+describe('unitFamily', () => {
+  it('maps g and kg to weight', () => {
+    expect(unitFamily('g')).toBe('weight');
+    expect(unitFamily('kg')).toBe('weight');
+  });
+  it('maps ml and l to volume', () => {
+    expect(unitFamily('ml')).toBe('volume');
+    expect(unitFamily('l')).toBe('volume');
+  });
+  it('lowercases and trims unknown units', () => {
+    expect(unitFamily(' Bund ')).toBe('bund');
+    expect(unitFamily('TL')).toBe('tl');
+    expect(unitFamily('Stück')).toBe('stück');
+  });
+  it('is case-insensitive for weight/volume', () => {
+    expect(unitFamily('Kg')).toBe('weight');
+    expect(unitFamily('ML')).toBe('volume');
+  });
+  it('returns empty string for null/undefined/empty', () => {
+    expect(unitFamily(null)).toBe('');
+    expect(unitFamily(undefined)).toBe('');
+    expect(unitFamily('')).toBe('');
+    expect(unitFamily('   ')).toBe('');
+  });
+});