diff --git a/app/conference_query.py b/app/conference_query.py
new file mode 100644
index 0000000..b661ede
--- /dev/null
+++ b/app/conference_query.py
@@ -0,0 +1,28 @@
+"""
+Query helpers for Conference-related aggregates.
+
+Peers created only for addConnection (P2P remote) are linked on conference.participants
+but often have no Session and no name; they are excluded. SFU endpoints (is_sfu) are
+excluded from participant totals — only human/clients with a session in the conference
+are counted.
+
+participants_count must use a Subquery (not Count on the outer queryset's participants
+relation): when /v1/conferences is filtered by participantId, the outer query joins
+participants and would otherwise restrict the aggregate to that single participant.
+"""
+
+from django.db.models import Count, IntegerField, OuterRef, Subquery
+
+from .models.participant import Participant
+
+PARTICIPANTS_COUNT_SUBQUERY = Subquery(
+    Participant.objects.filter(
+        conferences=OuterRef('pk'),
+        is_active=True,
+        is_sfu=False,
+        sessions__conference_id=OuterRef('pk'),
+    ).order_by().values('conferences').annotate(
+        cnt=Count('id', distinct=True),
+    ).values('cnt')[:1],
+    output_field=IntegerField(),
+)
diff --git a/app/tests/test_pr26_regressions.py b/app/tests/test_pr26_regressions.py
index 7e47b65..4106285 100644
--- a/app/tests/test_pr26_regressions.py
+++ b/app/tests/test_pr26_regressions.py
@@ -141,3 +141,41 @@ def test_gum_summary_skips_non_dict_issue_data(self):
         self.assertEqual(payload["total"], 1)
         self.assertEqual(payload["data"][0]["name"], "NotAllowedError")
         self.assertEqual(payload["data"][0]["count"], 1)
+
+    def test_conferences_participant_id_filter_preserves_full_participants_count(self):
+        """
+        When the conference list is filtered to one person (participantId),
+        participants_count must still reflect everyone in that conference, not 1.
+        """
+        conference = Conference.objects.create(
+            conference_id="conf-multi",
+            app=self.app,
+        )
+        participants = []
+        for i in range(3):
+            p = Participant.objects.create(
+                participant_id=f"user-{i}",
+                app=self.app,
+            )
+            p.conferences.add(conference)
+            Session.objects.create(
+                conference=conference,
+                participant=p,
+            )
+            participants.append(p)
+
+        response = self.client.get(
+            "/v1/conferences",
+            {
+                "appId": str(self.app.id),
+                "participantId": str(participants[0].id),
+                "limit": "50",
+            },
+        )
+
+        self.assertEqual(response.status_code, 200)
+        payload = json.loads(response.content)
+        self.assertEqual(payload["count"], 1)
+        self.assertEqual(len(payload["results"]), 1)
+        self.assertEqual(payload["results"][0]["id"], str(conference.id))
+        self.assertEqual(payload["results"][0]["participants_count"], 3)
diff --git a/app/views/conference_participant_count_summary_view.py b/app/views/conference_participant_count_summary_view.py
index 188d916..eed51f3 100644
--- a/app/views/conference_participant_count_summary_view.py
+++ b/app/views/conference_participant_count_summary_view.py
@@ -2,13 +2,11 @@
 from collections import Counter
 
 from django.core.exceptions import ValidationError
-from django.db.models import Count, IntegerField, OuterRef, Subquery
-
+from ..conference_query import PARTICIPANTS_COUNT_SUBQUERY
 from ..errors import INVALID_PARAMETERS, MISSING_PARAMETERS, PMError
 from ..summary_cache import cached_json
 from ..utils import JSONHttpResponse
 from ..models.conference import Conference
-from ..models.participant import Participant
 from .generic_view import GenericView
 
 
@@ -50,17 +48,7 @@ def compute():
             try:
                 per_conf = (Conference.objects
                     .filter(**filters)
-                    .annotate(
-                        participants_count=Subquery(
-                            Participant.objects.filter(
-                                conferences=OuterRef('pk'),
-                                is_active=True,
-                            ).order_by().values('conferences').annotate(
-                                cnt=Count('id', distinct=True)
-                            ).values('cnt')[:1],
-                            output_field=IntegerField(),
-                        ),
-                    )
+                    .annotate(participants_count=PARTICIPANTS_COUNT_SUBQUERY)
                     .values_list('participants_count', flat=True))
             except ValidationError:
                 raise PMError(status=400, app_error=INVALID_PARAMETERS)
diff --git a/app/views/conference_view.py b/app/views/conference_view.py
index 722899e..6c02fe3 100644
--- a/app/views/conference_view.py
+++ b/app/views/conference_view.py
@@ -1,14 +1,14 @@
 import datetime
 
 from django.core.exceptions import ValidationError
-from django.db.models import Count, Exists, IntegerField, OuterRef, Subquery
+from django.db.models import Exists, OuterRef
 
+from ..conference_query import PARTICIPANTS_COUNT_SUBQUERY
 from ..errors import (INVALID_PARAMETERS, CONFERENCE_NOT_FOUND,
                       MISSING_PARAMETERS, PMError)
 from ..utils import JSONHttpResponse, serialize, paginate_and_serialize
 from ..models.conference import Conference
 from ..models.issue import Issue
-from ..models.participant import Participant
 from .generic_view import GenericView
 
 class ConferencesView(GenericView):
@@ -63,15 +63,7 @@ def filter(cls, request):
                 has_warnings=Exists(
                     Issue.objects.filter(conference=OuterRef('pk'), type='w', is_active=True)
                 ),
-                participants_count=Subquery(
-                    Participant.objects.filter(
-                        conferences=OuterRef('pk'),
-                        is_active=True,
-                    ).order_by().values('conferences').annotate(
-                        cnt=Count('id', distinct=True)
-                    ).values('cnt')[:1],
-                    output_field=IntegerField(),
-                ),
+                participants_count=PARTICIPANTS_COUNT_SUBQUERY,
             )
             if filter_by_issue_code:
                 objs = objs.distinct()