diff --git a/src/Collections/TraversableUtilities.php b/src/Collections/TraversableUtilities.php
new file mode 100644
index 0000000..8d7921c
--- /dev/null
+++ b/src/Collections/TraversableUtilities.php
@@ -0,0 +1,27 @@
+<?php
+declare(strict_types=1);
+
+namespace Keruald\OmniTools\Collections;
+
+use Countable;
+use TypeError;
+
+class TraversableUtilities {
+
+    public static function count ($countable) : int {
+        if (is_array($countable)) {
+            return count($countable);
+        }
+
+        if ($countable instanceof Countable) {
+            return $countable->count();
+        }
+
+        if ($countable === null || $countable === false) {
+            return 0;
+        }
+
+        throw new TypeError;
+    }
+
+}
diff --git a/tests/Collections/TraversableUtilitiesTest.php b/tests/Collections/TraversableUtilitiesTest.php
new file mode 100644
index 0000000..d3c1073
--- /dev/null
+++ b/tests/Collections/TraversableUtilitiesTest.php
@@ -0,0 +1,55 @@
+<?php
+declare(strict_types=1);
+
+namespace Keruald\OmniTools\Tests\Collections;
+
+use Keruald\OmniTools\Collections\TraversableUtilities;
+use PHPUnit\Framework\TestCase;
+
+use Countable;
+
+class TraversableUtilitiesTest extends TestCase {
+
+    /**
+     * @dataProvider provideCountables
+     */
+    public function testCount ($expectedCount, $countable) {
+        $this->assertEquals(
+            $expectedCount, TraversableUtilities::count($countable)
+        );
+    }
+
+    /**
+     * @dataProvider provideNotCountables
+     */
+    public function testCountWithNotCountables ($notCountable) {
+        $this->expectException("TypeError");
+        TraversableUtilities::count($notCountable);
+    }
+
+    ///
+    /// Data providers
+    ///
+
+    public function provideCountables () : iterable {
+        yield [0, null];
+        yield [0, false];
+        yield [0, []];
+        yield [3, ["a", "b", "c"]];
+        yield [42, new class implements Countable {
+                public function count () : int {
+                    return 42;
+                }
+            }
+        ];
+    }
+
+    public function provideNotCountables () : iterable {
+        yield [true];
+        yield [new \stdClass];
+        yield [0];
+        yield [""];
+        yield ["abc"];
+    }
+
+}