diff --git a/back/boxtribute_server/business_logic/mobile_distribution/crud.py b/back/boxtribute_server/business_logic/mobile_distribution/crud.py
index cee78288fc..40f663da2c 100644
--- a/back/boxtribute_server/business_logic/mobile_distribution/crud.py
+++ b/back/boxtribute_server/business_logic/mobile_distribution/crud.py
@@ -21,6 +21,7 @@
 from ...models.definitions.product import Product
 from ...models.definitions.size import Size
 from ...models.definitions.size_range import SizeRange
+from ...models.definitions.size_range_size import SizeRangeSize
 from ...models.definitions.unboxed_items_collection import UnboxedItemsCollection
 from ...models.utils import utcnow
 from .exceptions import (
@@ -150,6 +151,7 @@ def set_products_for_packing_list(
         for product_id in product_ids_to_add:
             sizes = (
                 Size.select(Size.id)
+                .join(SizeRangeSize)
                 .join(SizeRange)
                 .join(Product)
                 .where(Product.id == product_id)
diff --git a/back/boxtribute_server/business_logic/warehouse/box/crud.py b/back/boxtribute_server/business_logic/warehouse/box/crud.py
index b20033e84a..894923ca7e 100644
--- a/back/boxtribute_server/business_logic/warehouse/box/crud.py
+++ b/back/boxtribute_server/business_logic/warehouse/box/crud.py
@@ -45,6 +45,7 @@
 from ....models.definitions.product import Product
 from ....models.definitions.qr_code import QrCode
 from ....models.definitions.size import Size
+from ....models.definitions.size_range_size import SizeRangeSize
 from ....models.definitions.tags_relation import TagsRelation
 from ....models.definitions.unit import Unit
 from ....models.utils import (
@@ -693,18 +694,21 @@ def create_boxes(*, user_id, data):
     sanitized_data, all_tag_ids = sanitize_input(data, new_tag_ids)
 
     # Build look-ups for products and their sizes
-    all_sizes = (
-        Product.select(Product.id, Product.size_range, Size.id, Size.label)
-        .left_outer_join(Size, on=(Product.size_range == Size.size_range))
-        .where(Product.id << product_ids)
+    product_rows = list(
+        Product.select(Product.id, Product.size_range).where(Product.id << product_ids)
     )
-    sizes_for_product = defaultdict(dict)
-    products = {}
-    for row in all_sizes:
-        products[row.id] = row
-        size = getattr(row, "size", None)
-        if size is not None:
-            sizes_for_product[row.id][size.label.lower()] = size.id
+    products = {p.id: p for p in product_rows}
+    size_range_ids = {p.size_range_id for p in product_rows if p.size_range_id}
+    sizes_for_size_range = defaultdict(dict)
+    for srs in (
+        SizeRangeSize.select(SizeRangeSize.size_range, Size.id, Size.label)
+        .join(Size)
+        .where(SizeRangeSize.size_range << size_range_ids)
+    ):
+        sizes_for_size_range[srs.size_range_id][srs.size.label.lower()] = srs.size_id
+    sizes_for_product = {
+        p.id: sizes_for_size_range.get(p.size_range_id, {}) for p in product_rows
+    }
 
     # Prepare units look-up
     units = {u.symbol: u for u in Unit.select()}
diff --git a/back/boxtribute_server/cron/data_faking.py b/back/boxtribute_server/cron/data_faking.py
index d894fc2da0..4870124bf2 100644
--- a/back/boxtribute_server/cron/data_faking.py
+++ b/back/boxtribute_server/cron/data_faking.py
@@ -62,6 +62,8 @@
 from ..models.definitions.product import Product
 from ..models.definitions.qr_code import QrCode
 from ..models.definitions.size import Size
+from ..models.definitions.size_range import SizeRange
+from ..models.definitions.size_range_size import SizeRangeSize
 from ..models.definitions.standard_product import StandardProduct
 from ..models.definitions.tag import Tag
 from ..models.definitions.transfer_agreement import TransferAgreement
@@ -750,9 +752,11 @@ def _generate_boxes(self):
                 Product.category,
                 fn.GROUP_CONCAT(Size.id).python_value(convert_ids).alias("size_ids"),
             )
+            .join(SizeRangeSize)
+            .join(SizeRange)
             .join(
                 Product,
-                on=(Product.size_range == Size.size_range),
+                on=(Product.size_range == SizeRange.id),
             )
             .group_by(Product.category)
             .namedtuples()
diff --git a/back/boxtribute_server/graph_ql/loaders.py b/back/boxtribute_server/graph_ql/loaders.py
index 2073014c38..9211706028 100644
--- a/back/boxtribute_server/graph_ql/loaders.py
+++ b/back/boxtribute_server/graph_ql/loaders.py
@@ -24,6 +24,7 @@
 from ..models.definitions.shipment_detail import ShipmentDetail
 from ..models.definitions.size import Size
 from ..models.definitions.size_range import SizeRange
+from ..models.definitions.size_range_size import SizeRangeSize
 from ..models.definitions.standard_product import StandardProduct
 from ..models.definitions.tag import Tag
 from ..models.definitions.tags_relation import TagsRelation
@@ -606,8 +607,8 @@ async def batch_load_fn(self, keys):
         authorize(permission="size:read")
         # Mapping of size range ID to list of sizes
         sizes = defaultdict(list)
-        for size in Size.select():
-            sizes[size.size_range_id].append(size)
+        for srs in SizeRangeSize.select(SizeRangeSize, Size).join(Size):
+            sizes[srs.size_range_id].append(srs.size)
         # Keys are in fact size range IDs. Return empty list if size range has no sizes
         return [sizes.get(i, []) for i in keys]
 
diff --git a/back/boxtribute_server/models/__init__.py b/back/boxtribute_server/models/__init__.py
index a5cbd4b269..7278af757d 100644
--- a/back/boxtribute_server/models/__init__.py
+++ b/back/boxtribute_server/models/__init__.py
@@ -25,6 +25,7 @@
 from .definitions.shipment_detail import ShipmentDetail
 from .definitions.size import Size
 from .definitions.size_range import SizeRange
+from .definitions.size_range_size import SizeRangeSize
 from .definitions.standard_product import StandardProduct
 from .definitions.tag import Tag
 from .definitions.tags_relation import TagsRelation
@@ -71,6 +72,7 @@
     ShipmentDetail,
     Size,
     SizeRange,
+    SizeRangeSize,
     StandardProduct,
     Tag,
     TagsRelation,
diff --git a/back/boxtribute_server/models/definitions/size.py b/back/boxtribute_server/models/definitions/size.py
index a7fd4554c9..370a950fc1 100644
--- a/back/boxtribute_server/models/definitions/size.py
+++ b/back/boxtribute_server/models/definitions/size.py
@@ -1,8 +1,7 @@
-from peewee import CharField, DateTimeField, IntegerField
+from peewee import CharField, DateTimeField
 
 from ..fields import UIntForeignKeyField
 from . import Model
-from .size_range import SizeRange
 from .user import User
 
 
@@ -26,15 +25,6 @@ class Size(Model):
         on_delete="SET NULL",
         on_update="CASCADE",
     )
-    seq = IntegerField(null=True)
-    size_range = UIntForeignKeyField(
-        column_name="sizegroup_id",
-        field="id",
-        model=SizeRange,
-        null=True,
-        on_update="CASCADE",
-        object_id_name="size_range_id",
-    )
 
     class Meta:
         table_name = "sizes"
diff --git a/back/boxtribute_server/models/definitions/size_range_size.py b/back/boxtribute_server/models/definitions/size_range_size.py
new file mode 100644
index 0000000000..4500139f46
--- /dev/null
+++ b/back/boxtribute_server/models/definitions/size_range_size.py
@@ -0,0 +1,29 @@
+from peewee import CompositeKey
+
+from ..fields import UIntForeignKeyField
+from . import Model
+from .size import Size
+from .size_range import SizeRange
+
+
+class SizeRangeSize(Model):
+    size = UIntForeignKeyField(
+        column_name="size_id",
+        field="id",
+        model=Size,
+        object_id_name="size_id",
+        on_delete="CASCADE",
+        on_update="CASCADE",
+    )
+    size_range = UIntForeignKeyField(
+        column_name="sizegroup_id",
+        field="id",
+        model=SizeRange,
+        object_id_name="size_range_id",
+        on_delete="CASCADE",
+        on_update="CASCADE",
+    )
+
+    class Meta:
+        table_name = "sizes_sizegroup"
+        primary_key = CompositeKey("size", "size_range")
diff --git a/back/test/data/__init__.py b/back/test/data/__init__.py
index 0e45c73777..d6c3bb21b6 100644
--- a/back/test/data/__init__.py
+++ b/back/test/data/__init__.py
@@ -257,6 +257,7 @@
     "product",
     "size",
     "unit",
+    "size_range_size",
     "box",
     "beneficiary",
     "transfer_agreement",
diff --git a/back/test/data/size.py b/back/test/data/size.py
index d8090600da..deb1b2fe3c 100644
--- a/back/test/data/size.py
+++ b/back/test/data/size.py
@@ -1,19 +1,17 @@
 import pytest
 from boxtribute_server.models.definitions.size import Size
 
-from .size_range import data as size_range_data
-
 
 def default_size_data():
-    return {"id": 1, "label": "small", "size_range": size_range_data()[0]["id"]}
+    return {"id": 1, "label": "small"}
 
 
 def another_size_data():
-    return {"id": 2, "label": "medium", "size_range": size_range_data()[0]["id"]}
+    return {"id": 2, "label": "medium"}
 
 
 def mixed_size_data():
-    return {"id": 3, "label": "Mixed", "size_range": size_range_data()[0]["id"]}
+    return {"id": 3, "label": "Mixed"}
 
 
 @pytest.fixture
diff --git a/back/test/data/size_range_size.py b/back/test/data/size_range_size.py
new file mode 100644
index 0000000000..4e10228a16
--- /dev/null
+++ b/back/test/data/size_range_size.py
@@ -0,0 +1,17 @@
+from boxtribute_server.models.definitions.size_range_size import SizeRangeSize
+
+from .size import another_size_data, default_size_data, mixed_size_data
+from .size_range import data as size_range_data
+
+
+def data():
+    size_range_id = size_range_data()[0]["id"]
+    return [
+        {"size": default_size_data()["id"], "size_range": size_range_id},
+        {"size": another_size_data()["id"], "size_range": size_range_id},
+        {"size": mixed_size_data()["id"], "size_range": size_range_id},
+    ]
+
+
+def create():
+    SizeRangeSize.insert_many(data()).execute()