diff --git a/subiquity/common/filesystem/manipulator.py b/subiquity/common/filesystem/manipulator.py
index 6faa2c60..cffac81d 100644
--- a/subiquity/common/filesystem/manipulator.py
+++ b/subiquity/common/filesystem/manipulator.py
@@ -15,74 +15,15 @@
 
 import logging
 
-import attr
-
-from subiquity.common.filesystem import boot, gaps
+from subiquity.common.filesystem import boot, gaps, sizes
 from subiquity.common.types import Bootloader
 from subiquity.models.filesystem import (
     align_up,
-    MiB,
     Partition,
     )
 
 log = logging.getLogger('subiquity.common.filesystem.manipulator')
 
-BIOS_GRUB_SIZE_BYTES = 1 * MiB
-PREP_GRUB_SIZE_BYTES = 8 * MiB
-
-
-@attr.s(auto_attribs=True)
-class PartitionScaleFactors:
-    minimum: int
-    priority: int
-    maximum: int
-
-
-uefi_scale = PartitionScaleFactors(
-        minimum=538 * MiB,
-        priority=538,
-        maximum=1075 * MiB)
-bootfs_scale = PartitionScaleFactors(
-        minimum=768 * MiB,
-        priority=1024,
-        maximum=1536 * MiB)
-rootfs_scale = PartitionScaleFactors(
-        minimum=900 * MiB,
-        priority=10000,
-        maximum=-1)
-
-
-def scale_partitions(all_factors, disk_size):
-    """for the list of scale factors, provide list of scaled partition size.
-    Assumes at most one scale factor with maximum==-1, and
-    disk_size is at least as big as the sum of all partition minimums.
-    The scale factor with maximum==-1 is given all remaining disk space."""
-    ret = []
-    sum_priorities = sum([factor.priority for factor in all_factors])
-    for cur in all_factors:
-        scaled = int((disk_size / sum_priorities) * cur.priority)
-        if scaled < cur.minimum:
-            ret.append(cur.minimum)
-        elif scaled > cur.maximum:
-            ret.append(cur.maximum)
-        else:
-            ret.append(scaled)
-    if -1 in ret:
-        used = sum(filter(lambda x: x != -1, ret))
-        idx = ret.index(-1)
-        ret[idx] = disk_size - used
-    return ret
-
-
-def get_efi_size(disk):
-    all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
-    return scale_partitions(all_factors, disk.size)[0]
-
-
-def get_bootfs_size(disk):
-    all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
-    return scale_partitions(all_factors, disk.size)[1]
-
 
 class FilesystemManipulator:
 
@@ -157,7 +98,7 @@ class FilesystemManipulator:
     def _create_boot_partition(self, disk):
         bootloader = self.model.bootloader
         if bootloader == Bootloader.UEFI:
-            part_size = get_efi_size(disk)
+            part_size = sizes.get_efi_size(disk)
             log.debug('_create_boot_partition - adding EFI partition')
             spec = dict(size=part_size, fstype='fat32')
             if self.model._mount_for_path("/boot/efi") is None:
@@ -168,7 +109,7 @@ class FilesystemManipulator:
             log.debug('_create_boot_partition - adding PReP partition')
             part = self._create_boot_with_resize(
                 disk,
-                dict(size=PREP_GRUB_SIZE_BYTES, fstype=None, mount=None),
+                dict(size=sizes.PREP_GRUB_SIZE_BYTES, fstype=None, mount=None),
                 # must be wiped or grub-install will fail
                 wipe='zero',
                 flag='prep', grub_device=True)
@@ -176,7 +117,7 @@ class FilesystemManipulator:
             log.debug('_create_boot_partition - adding bios_grub partition')
             part = self._create_boot_with_resize(
                 disk,
-                dict(size=BIOS_GRUB_SIZE_BYTES, fstype=None, mount=None),
+                dict(size=sizes.BIOS_GRUB_SIZE_BYTES, fstype=None, mount=None),
                 flag='bios_grub')
             disk.grub_device = True
         return part
diff --git a/subiquity/common/filesystem/sizes.py b/subiquity/common/filesystem/sizes.py
new file mode 100644
index 00000000..22edd1be
--- /dev/null
+++ b/subiquity/common/filesystem/sizes.py
@@ -0,0 +1,77 @@
+# Copyright 2022 Canonical, Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import attr
+
+from subiquity.models.filesystem import (
+    MiB,
+    )
+
+
+BIOS_GRUB_SIZE_BYTES = 1 * MiB
+PREP_GRUB_SIZE_BYTES = 8 * MiB
+
+
+@attr.s(auto_attribs=True)
+class PartitionScaleFactors:
+    minimum: int
+    priority: int
+    maximum: int
+
+
+uefi_scale = PartitionScaleFactors(
+        minimum=538 * MiB,
+        priority=538,
+        maximum=1075 * MiB)
+bootfs_scale = PartitionScaleFactors(
+        minimum=768 * MiB,
+        priority=1024,
+        maximum=1536 * MiB)
+rootfs_scale = PartitionScaleFactors(
+        minimum=900 * MiB,
+        priority=10000,
+        maximum=-1)
+
+
+def scale_partitions(all_factors, disk_size):
+    """for the list of scale factors, provide list of scaled partition size.
+    Assumes at most one scale factor with maximum==-1, and
+    disk_size is at least as big as the sum of all partition minimums.
+    The scale factor with maximum==-1 is given all remaining disk space."""
+    ret = []
+    sum_priorities = sum([factor.priority for factor in all_factors])
+    for cur in all_factors:
+        scaled = int((disk_size / sum_priorities) * cur.priority)
+        if scaled < cur.minimum:
+            ret.append(cur.minimum)
+        elif scaled > cur.maximum:
+            ret.append(cur.maximum)
+        else:
+            ret.append(scaled)
+    if -1 in ret:
+        used = sum(filter(lambda x: x != -1, ret))
+        idx = ret.index(-1)
+        ret[idx] = disk_size - used
+    return ret
+
+
+def get_efi_size(disk):
+    all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
+    return scale_partitions(all_factors, disk.size)[0]
+
+
+def get_bootfs_size(disk):
+    all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
+    return scale_partitions(all_factors, disk.size)[1]
diff --git a/subiquity/common/filesystem/tests/test_manipulator.py b/subiquity/common/filesystem/tests/test_manipulator.py
index f8a4050c..0f1c6d7b 100644
--- a/subiquity/common/filesystem/tests/test_manipulator.py
+++ b/subiquity/common/filesystem/tests/test_manipulator.py
@@ -19,15 +19,7 @@ from subiquity.common.filesystem.actions import (
     DeviceAction,
     )
 from subiquity.common.filesystem import gaps
-from subiquity.common.filesystem.manipulator import (
-    bootfs_scale,
-    FilesystemManipulator,
-    get_efi_size,
-    get_bootfs_size,
-    PartitionScaleFactors,
-    scale_partitions,
-    uefi_scale,
-    )
+from subiquity.common.filesystem.manipulator import FilesystemManipulator
 from subiquity.models.tests.test_filesystem import (
     make_disk,
     make_model,
@@ -242,57 +234,3 @@ class TestFilesystemManipulator(unittest.TestCase):
             manipulator.add_boot_disk(disk1)
             part = gaps.parts_and_gaps(disk1)[0]
             self.assertEqual(1024 * 1024, part.offset)
-
-
-class TestPartitionSizeScaling(unittest.TestCase):
-    def test_scale_factors(self):
-        psf = [
-            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
-            PartitionScaleFactors(minimum=1000, priority=9500, maximum=-1),
-        ]
-
-        # match priorities, should get same values back
-        self.assertEqual([500, 9500], scale_partitions(psf, 10000))
-
-        # half priorities, should be scaled
-        self.assertEqual([250, 4750], scale_partitions(psf, 5000))
-
-        # hit max on first partition, second should use rest of space
-        self.assertEqual([500, 19500], scale_partitions(psf, 20000))
-
-        # minimums
-        self.assertEqual([100, 1000], scale_partitions(psf, 1100))
-
-        # ints
-        self.assertEqual([105, 1996], scale_partitions(psf, 2101))
-
-    def test_no_max_equal_minus_one(self):
-        psf = [
-            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
-            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
-        ]
-
-        self.assertEqual([500, 500], scale_partitions(psf, 2000))
-
-    def test_efi(self):
-        manipulator = make_manipulator(Bootloader.UEFI)
-        tests = [
-            # something large to hit maximums
-            (30 << 30, uefi_scale.maximum, bootfs_scale.maximum),
-            # and something small to hit minimums
-            (8 << 30, uefi_scale.minimum, bootfs_scale.minimum),
-        ]
-        for disk_size, uefi, bootfs in tests:
-            disk = make_disk(manipulator.model, preserve=True, size=disk_size)
-            self.assertEqual(uefi, get_efi_size(disk))
-            self.assertEqual(bootfs, get_bootfs_size(disk))
-
-        # something in between for scaling
-        disk_size = 15 << 30
-        disk = make_disk(manipulator.model, preserve=True, size=disk_size)
-        efi_size = get_efi_size(disk)
-        self.assertTrue(uefi_scale.maximum > efi_size)
-        self.assertTrue(efi_size > uefi_scale.minimum)
-        bootfs_size = get_bootfs_size(disk)
-        self.assertTrue(bootfs_scale.maximum > bootfs_size)
-        self.assertTrue(bootfs_size > bootfs_scale.minimum)
diff --git a/subiquity/common/filesystem/tests/test_sizes.py b/subiquity/common/filesystem/tests/test_sizes.py
new file mode 100644
index 00000000..277b915f
--- /dev/null
+++ b/subiquity/common/filesystem/tests/test_sizes.py
@@ -0,0 +1,82 @@
+# Copyright 2022 Canonical, Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+
+from subiquity.common.filesystem.sizes import (
+    bootfs_scale,
+    get_efi_size,
+    get_bootfs_size,
+    PartitionScaleFactors,
+    scale_partitions,
+    uefi_scale,
+    )
+from subiquity.common.filesystem.tests.test_manipulator import make_manipulator
+from subiquity.models.filesystem import Bootloader
+from subiquity.models.tests.test_filesystem import make_disk
+
+
+class TestPartitionSizeScaling(unittest.TestCase):
+    def test_scale_factors(self):
+        psf = [
+            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
+            PartitionScaleFactors(minimum=1000, priority=9500, maximum=-1),
+        ]
+
+        # match priorities, should get same values back
+        self.assertEqual([500, 9500], scale_partitions(psf, 10000))
+
+        # half priorities, should be scaled
+        self.assertEqual([250, 4750], scale_partitions(psf, 5000))
+
+        # hit max on first partition, second should use rest of space
+        self.assertEqual([500, 19500], scale_partitions(psf, 20000))
+
+        # minimums
+        self.assertEqual([100, 1000], scale_partitions(psf, 1100))
+
+        # ints
+        self.assertEqual([105, 1996], scale_partitions(psf, 2101))
+
+    def test_no_max_equal_minus_one(self):
+        psf = [
+            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
+            PartitionScaleFactors(minimum=100, priority=500, maximum=500),
+        ]
+
+        self.assertEqual([500, 500], scale_partitions(psf, 2000))
+
+    def test_efi(self):
+        manipulator = make_manipulator(Bootloader.UEFI)
+        tests = [
+            # something large to hit maximums
+            (30 << 30, uefi_scale.maximum, bootfs_scale.maximum),
+            # and something small to hit minimums
+            (8 << 30, uefi_scale.minimum, bootfs_scale.minimum),
+        ]
+        for disk_size, uefi, bootfs in tests:
+            disk = make_disk(manipulator.model, preserve=True, size=disk_size)
+            self.assertEqual(uefi, get_efi_size(disk))
+            self.assertEqual(bootfs, get_bootfs_size(disk))
+
+        # something in between for scaling
+        disk_size = 15 << 30
+        disk = make_disk(manipulator.model, preserve=True, size=disk_size)
+        efi_size = get_efi_size(disk)
+        self.assertTrue(uefi_scale.maximum > efi_size)
+        self.assertTrue(efi_size > uefi_scale.minimum)
+        bootfs_size = get_bootfs_size(disk)
+        self.assertTrue(bootfs_scale.maximum > bootfs_size)
+        self.assertTrue(bootfs_size > bootfs_scale.minimum)
diff --git a/subiquity/server/controllers/filesystem.py b/subiquity/server/controllers/filesystem.py
index 3bb5beb7..8be3d947 100644
--- a/subiquity/server/controllers/filesystem.py
+++ b/subiquity/server/controllers/filesystem.py
@@ -41,10 +41,9 @@ from subiquity.common.errorreport import ErrorReportKind
 from subiquity.common.filesystem.actions import (
     DeviceAction,
     )
-from subiquity.common.filesystem import boot, gaps, labels
+from subiquity.common.filesystem import boot, gaps, labels, sizes
 from subiquity.common.filesystem.manipulator import (
     FilesystemManipulator,
-    get_bootfs_size,
 )
 from subiquity.common.types import (
     Bootloader,
@@ -146,7 +145,7 @@ class FilesystemController(SubiquityController, FilesystemManipulator):
         gap = gaps.largest_gap(disk)
         self.create_partition(
             device=disk, gap=gap, spec=dict(
-                size=get_bootfs_size(disk),
+                size=sizes.get_bootfs_size(disk),
                 fstype="ext4",
                 mount='/boot'
                 ))