diff --git a/src/index.js b/src/index.js
index da2fd1a..1f5448c 100644
--- a/src/index.js
+++ b/src/index.js
@@ -55,7 +55,7 @@ function bindLocaleSwitcher(initialValue) {
         i18next
             .changeLanguage(e.target.value)
             .then(translatePageElements)
-            .then(update);
+            .then(updateCageCheck);
     };
 }
 
@@ -63,7 +63,7 @@ function bindLocaleSwitcher(initialValue) {
     await initI18next();
     translatePageElements();
     bindLocaleSwitcher(i18next.resolvedLanguage);
-    update();
+    updateCageCheck();
 })();
 
 //////////
@@ -148,7 +148,20 @@ class Validator {
         if (numOfRats < 3 || numOfRats > 15) {
             throw new Error("This formula works only from 3 to 15 rats");
         }
-        return MINIMUM_AREA_THREE_RATS + (numOfRats - 3) * AREA_PER_ADDITIONAL_RAT;
+        return MINIMUM_AREA_THREE_RATS + (numOfRats - 3.0) * AREA_PER_ADDITIONAL_RAT;
+    }
+
+    allowedNumberOfRats(overallArea) {
+        /*
+        Calculates the number of rats that are allowed for a certain overall area.
+         */
+        let result = 3.0 + (overallArea-MINIMUM_AREA_THREE_RATS) / AREA_PER_ADDITIONAL_RAT;
+        console.log(`Area left: ${overallArea-MINIMUM_AREA_THREE_RATS}`);
+        console.log(`Result: ${result}`);
+        if (result < 3) {
+            throw new Error("Cages must be for three rats or more");
+        }
+        return result;
     }
 
     failCageNumberIndependent(dimensions, numFullFloors) {
@@ -181,6 +194,11 @@ class Validator {
         return failedCriteria;
     }
 
+    getOverallArea(dimensions, numFullFloors) {
+        const baseArea = dimensions.depth * dimensions.width;
+        return baseArea * numFullFloors
+    }
+
     cageCheck(dimensions, numRats, numFullFloors) {
         /*
         Function that checks a cage based on overall criteria and the number of rats.
@@ -191,9 +209,9 @@ class Validator {
             failedCriteria[FAILED_NUM_RATS] = this.FAIL_CRITERIA[FAILED_NUM_RATS];
         }
 
-        const areaNeeded = this.overallAreaNeeded(numRats);
-        const baseArea = dimensions.depth * dimensions.width;
-        if (baseArea * numFullFloors < areaNeeded) {
+        const overallArea = this.getOverallArea(dimensions, numFullFloors);
+        const overallAreaNeeded = this.overallAreaNeeded(numRats);
+        if (overallArea < overallAreaNeeded) {
             failedCriteria[FAILED_OVERALL_AREA] = this.FAIL_CRITERIA[FAILED_OVERALL_AREA];
         }
 
@@ -225,13 +243,30 @@ class Dimensions {
 // DOCUMENT INTERACTION //
 //////////////////////////
 
-const inputWidth = document.getElementById("width");
-inputWidth.onchange = updateViaManualMeasurements;
-const inputDepth = document.getElementById("depth");
-inputDepth.onchange = updateViaManualMeasurements;
-const inputHeight = document.getElementById("height");
-inputHeight.onchange = updateViaManualMeasurements;
+const numRatsCalculatorInputWidth = document.getElementById("num-rats-width");
+numRatsCalculatorInputWidth.onchange = updateNumRatsCalculator;
+const numRatsCalculatorInputDepth = document.getElementById("num-rats-depth");
+numRatsCalculatorInputDepth.onchange = updateNumRatsCalculator;
+const numRatsCalculatorInputHeight = document.getElementById("num-rats-height");
+numRatsCalculatorInputHeight.onchange = updateNumRatsCalculator;
 
+let numRatsNumFullFloors = document.getElementById("num-rats-numFullFloors");
+numRatsNumFullFloors.oninput = function () {
+    updateNumRatsCalculator();
+}
+
+
+const inputWidth = document.getElementById("width");
+inputWidth.onchange = updateCageCheck;
+const inputDepth = document.getElementById("depth");
+inputDepth.onchange = updateCageCheck;
+const inputHeight = document.getElementById("height");
+inputHeight.onchange = updateCageCheck;
+
+let fullFloorNum = document.getElementById("numFullFloors");
+fullFloorNum.oninput = function () {
+    updateCageCheck();
+}
 
 
 let labelNumRats = document.getElementById("labelNumRats");
@@ -239,14 +274,9 @@ let labelNumRats = document.getElementById("labelNumRats");
 let ratSlider = document.getElementById("numRats");
 
 ratSlider.oninput = function () {
-    update();
+    updateCageCheck();
 }
 
-// Full floor functions
-let fullFloorNum = document.getElementById("numFullFloors");
-fullFloorNum.oninput = function () {
-    update();
-}
 
 function getResultFromChecks(checks) {
     if (Object.keys(checks).length > 0) {
@@ -265,11 +295,7 @@ function getResultFromChecks(checks) {
 
 }
 
-function updateViaManualMeasurements() {
-    update();
-}
-
-function update() {
+function updateCageCheck() {
     labelNumRats.innerHTML = i18next.t("cage-for-x-rats", {"num_rats": ratSlider.value});
 
     const width = inputWidth.value
@@ -285,3 +311,38 @@ function update() {
     resultsDiv.innerHTML = "";
     resultsDiv.appendChild(result);
 }
+
+function updateNumRatsCalculator() {
+
+    const width = numRatsCalculatorInputWidth.value
+    const depth = numRatsCalculatorInputDepth.value
+    const height = numRatsCalculatorInputHeight.value
+    const dimensions = new Dimensions(width / 100, depth / 100, height / 100);
+    const validator = new Validator();
+    const failed_checks = validator.failCageNumberIndependent(dimensions, fullFloorNum.value);
+
+    let overallArea = validator.getOverallArea(dimensions, numRatsNumFullFloors.value);
+    let allowedNumRats;
+    try {
+        allowedNumRats = validator.allowedNumberOfRats(overallArea);
+    } catch (e) {
+        console.log(e);
+        failed_checks[FAILED_BASE_AREA] = validator.FAIL_CRITERIA[FAILED_OVERALL_AREA];
+        allowedNumRats = 0;
+    }
+
+
+    console.log(`Allowed number: ${allowedNumRats}`);
+
+    let resultsDiv = document.getElementById("num-rats-resultsDiv");
+
+    const result = getResultFromChecks(failed_checks);
+
+    resultsDiv.innerHTML = "";
+    const p = document.createElement('p');
+    p.textContent = i18next.t("cage-for-x-rats", {"num_rats": allowedNumRats});
+    resultsDiv.appendChild(p);
+    resultsDiv.appendChild(result);
+}
+
+const validator = new Validator();
\ No newline at end of file