diff --git a/zetta_utils/geometry/bbox.py b/zetta_utils/geometry/bbox.py
index 8a8fa7a2c..f01a13dd3 100644
--- a/zetta_utils/geometry/bbox.py
+++ b/zetta_utils/geometry/bbox.py
@@ -1,6 +1,7 @@
 # pylint: disable=missing-docstring, no-else-raise
 from __future__ import annotations
 
+import math
 from itertools import product
 from math import floor
 from typing import Literal, Optional, Sequence, Union, cast
@@ -205,24 +206,23 @@ def get_slice(
             return slice(dim_range_start_raw, dim_range_end_raw)
 
         if not allow_slice_rounding:
-            if dim_range_start_raw != round(dim_range_start_raw):
+            if dim_range_start_raw != math.floor(dim_range_start_raw):
                 raise ValueError(
                     f"{self} results in slice_start == "
                     f"{dim_range_start_raw} along dimension {dim} "
                     f"at resolution == {resolution} while "
                     "`allow_slice_rounding` == False."
                 )
-            if dim_range_end_raw != round(dim_range_end_raw):
+            if dim_range_end_raw != math.ceil(dim_range_end_raw):
                 raise ValueError(
                     f"{self} results in slice_end == "
                     f"{dim_range_end_raw} along dimension {dim} "
                     f"at resolution == {resolution} while "
                     "`allow_slice_rounding` == False."
                 )
-        slice_length = int(round(dim_range_end_raw - dim_range_start_raw))
         result = slice(
-            floor(dim_range_start_raw),
-            floor(dim_range_start_raw) + slice_length,
+            math.floor(dim_range_start_raw),
+            math.ceil(dim_range_end_raw),
         )
         return result
 
@@ -576,9 +576,10 @@ def pformat(self, resolution: Optional[Sequence[float]] = None) -> str:  # pragm
             f"({s.join([str(slice.stop) for slice in slices])})"
         )
 
-    def get_size(self) -> Union[int, float]:  # pragma: no cover
+    def get_size(
+        self, resolution: Sequence[float] = (1, 1, 1)
+    ) -> Union[int, float]:  # pragma: no cover
         """Returns the volume of the box, in base units (i.e. `nm^3`)."""
-        resolution = (1, 1, 1)
         slices = self.to_slices(resolution, round_to_int=False)
         size = 1
         for _, slc in enumerate(slices):