diff --git a/backend/package-lock.json b/backend/package-lock.json
index 31d92f6..ec32ca8 100644
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
@@ -12,6 +12,7 @@
         "cheerio": "^1.0.0-rc.12",
         "cors": "^2.8.5",
         "dotenv": "^16.3.1",
+        "expr-eval": "^2.0.2",
         "express": "^4.18.2",
         "graphql": "^16.8.1",
         "graphql-request": "^6.1.0",
@@ -2782,6 +2783,12 @@
         "node": "^14.15.0 || ^16.10.0 || >=18.0.0"
       }
     },
+    "node_modules/expr-eval": {
+      "version": "2.0.2",
+      "resolved": "https://registry.npmjs.org/expr-eval/-/expr-eval-2.0.2.tgz",
+      "integrity": "sha512-4EMSHGOPSwAfBiibw3ndnP0AvjDWLsMvGOvWEZ2F96IGk0bIVdjQisOHxReSkE13mHcfbuCiXw+G4y0zv6N8Eg==",
+      "license": "MIT"
+    },
     "node_modules/express": {
       "version": "4.21.2",
       "resolved": "https://registry.npmjs.org/express/-/express-4.21.2.tgz",
diff --git a/backend/package.json b/backend/package.json
index b96cee4..7c38461 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -17,6 +17,7 @@
     "cheerio": "^1.0.0-rc.12",
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
+    "expr-eval": "^2.0.2",
     "express": "^4.18.2",
     "graphql": "^16.8.1",
     "graphql-request": "^6.1.0",
diff --git a/backend/src/services/smartPackageManagementService.js b/backend/src/services/smartPackageManagementService.js
index 5b598de..b40b404 100644
--- a/backend/src/services/smartPackageManagementService.js
+++ b/backend/src/services/smartPackageManagementService.js
@@ -1565,15 +1565,11 @@ class SmartPackageManagementService {
       console.log('🧮 [FORMULA] After substitution:', expr);
       logger.info('After variable substitution:', { expr, geometry: { length: geometry.length_main, width: geometry.width_main, area: geometry.total_area } });
       
-      // Evaluer matematisk udtryk (sikker måde)
-      // Tillad kun tal, +, -, *, /, (, ), .
-      if (!/^[\d\s+\-*/.()]+$/.test(expr)) {
-        console.log('⚠️ [FORMULA] Invalid expression:', expr);
-        logger.warn('Invalid formula expression:', { expr, original: formula });
-        return 1; // Fallback
-      }
-      
-      const result = eval(expr);
+      // Evaluer matematisk udtryk via sikker parser
+      const { Parser } = require('expr-eval');
+      const parser = new Parser({});
+      const parsed = parser.parse(String(expr || '0'));
+      const result = Number(parsed.evaluate(variables)) || 0;
       console.log('✅ [FORMULA] Result:', result);
       logger.info('Formula result:', { result, expr });
       return Math.max(0, result); // Ingen negative værdier
diff --git a/backend/unified-server.js b/backend/unified-server.js
index 261123f..f7b493c 100644
--- a/backend/unified-server.js
+++ b/backend/unified-server.js
@@ -6,6 +6,7 @@ const http = require('http');
 const { Server } = require('socket.io');
 const jwt = require('jsonwebtoken');
 const axios = require('axios');
+const { Parser } = require('expr-eval');
 // const HistoricalQuoteCalculator = require('./historical-quote-calculator.js'); // Temporarily disabled
 
 // Load environment variables FIRST
@@ -211,14 +212,23 @@ async function calculateMaterialQuantities(projectId, geometry) {
     
     for (const formula of formulas) {
       try {
-        // Create safe evaluation context
+        // Build evaluation context (support both GEOM.xxx and direct vars)
         const GEOM = {
-          area_m2: geometry.area_m2 || 0,
-          vindskede_lbm: geometry.vindskede_lbm || 0
+          area_m2: Number(geometry.area_m2) || 0,
+          vindskede_lbm: Number(geometry.vindskede_lbm) || 0
         };
-        
-        // Evaluate formula safely
-        const calculatedValue = eval(formula.qty_formula);
+        const vars = { GEOM, ...GEOM };
+
+        // Evaluate formula using a safe math parser
+        let calculatedValue = 0;
+        try {
+          const parser = new Parser({});
+          const expr = parser.parse(String(formula.qty_formula || '0'));
+          calculatedValue = Number(expr.evaluate(vars)) || 0;
+        } catch (e) {
+          console.error(`❌ Formula parse/eval error for ${formula.material_sku}:`, e.message);
+          calculatedValue = 0;
+        }
         const quantity = Math.ceil(calculatedValue * formula.unit_per_formula * formula.waste_factor);
         
         if (quantity > 0) {