diff --git a/egsis/metrics.py b/egsis/metrics.py
index d8d94a5..6e8c605 100644
--- a/egsis/metrics.py
+++ b/egsis/metrics.py
@@ -25,7 +25,7 @@ def iou(y_true: np.ndarray, y_pred: np.ndarray) -> float:
 def f1(y_true: np.ndarray, y_pred: np.ndarray) -> float:
     _check_if_they_are_binarized(y_true, y_pred)
     intersection = y_true & y_pred
-    total_size = y_true.size + y_pred.size
+    total_size = y_true.sum() + y_pred.sum()
     return (2 * intersection.sum()) / total_size
 
 
diff --git a/tests/test_metrics.py b/tests/test_metrics.py
index 3151853..7cf57e3 100644
--- a/tests/test_metrics.py
+++ b/tests/test_metrics.py
@@ -32,7 +32,7 @@ def test_iou(x, y):
 
 
 def test_f1(x, y):
-    assert metrics.f1(x, y) == pytest.approx(0.11111, 0.001)
+    assert metrics.f1(x, y) == pytest.approx(0.33333, 0.001)
 
 
 def test_iou_raise_error_on_non_binarized_labels(x, y):