diff --git a/apps/backend/app/api/deps.py b/apps/backend/app/api/deps.py
index 4dc32cb..3407de3 100644
--- a/apps/backend/app/api/deps.py
+++ b/apps/backend/app/api/deps.py
@@ -23,9 +23,12 @@ from app.core.security import decode_access_token as decode_token
 from app.db.session import get_session
 from app.repositories.audit_log import AuditLogRepository
 from app.repositories.login_attempt import LoginAttemptRepository
+from app.repositories.reading import ReadingRepository
 from app.repositories.refresh_token import RefreshTokenRepository
+from app.repositories.site import SiteRepository
 from app.repositories.user import UserRepository
 from app.services.auth import AuthService, LoginPolicy
+from app.services.stats import StatsService
 from app.services.user import UserService
 
 SessionDep = Annotated[AsyncSession, Depends(get_session)]
@@ -131,6 +134,13 @@ def get_user_service(
 UserServiceDep = Annotated[UserService, Depends(get_user_service)]
 
 
+def get_stats_service(session: SessionDep) -> StatsService:
+    return StatsService(sites=SiteRepository(session), readings=ReadingRepository(session))
+
+
+StatsServiceDep = Annotated[StatsService, Depends(get_stats_service)]
+
+
 async def get_current_principal(
     credentials: CredentialsDep,
     session: SessionDep,
diff --git a/apps/backend/app/api/v1/endpoints/stats.py b/apps/backend/app/api/v1/endpoints/stats.py
new file mode 100644
index 0000000..5a8502e
--- /dev/null
+++ b/apps/backend/app/api/v1/endpoints/stats.py
@@ -0,0 +1,16 @@
+from fastapi import APIRouter
+
+from app.api.deps import LecteurDep, StatsServiceDep
+from app.schemas.stats import StatsSummaryResponse
+
+router = APIRouter()
+
+
+@router.get(
+    "/summary",
+    response_model=StatsSummaryResponse,
+    summary="Résume la consommation instantanée du parc",
+)
+async def get_summary(_: LecteurDep, service: StatsServiceDep) -> StatsSummaryResponse:
+    resume = await service.summary()
+    return StatsSummaryResponse.model_validate(resume)
diff --git a/apps/backend/app/api/v1/router.py b/apps/backend/app/api/v1/router.py
index 76e6f28..06e8852 100644
--- a/apps/backend/app/api/v1/router.py
+++ b/apps/backend/app/api/v1/router.py
@@ -1,8 +1,9 @@
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import auth, health, users
+from app.api.v1.endpoints import auth, health, stats, users
 
 api_router = APIRouter()
 api_router.include_router(health.router, prefix="/health", tags=["health"])
 api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
 api_router.include_router(users.router, prefix="/users", tags=["users"])
+api_router.include_router(stats.router, prefix="/stats", tags=["stats"])
diff --git a/apps/backend/app/repositories/reading.py b/apps/backend/app/repositories/reading.py
new file mode 100644
index 0000000..5424b46
--- /dev/null
+++ b/apps/backend/app/repositories/reading.py
@@ -0,0 +1,21 @@
+from collections.abc import Sequence
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Reading
+
+
+class ReadingRepository:
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    async def latest_by_site(self) -> Sequence[Reading]:
+        # `.distinct(site_id)` compile en `DISTINCT ON (site_id)` sous PostgreSQL : une seule
+        # ligne par site, la plus récente grâce à l'ordre composite qui suit.
+        requete = (
+            select(Reading)
+            .distinct(Reading.site_id)
+            .order_by(Reading.site_id, Reading.timestamp.desc())
+        )
+        return (await self._session.execute(requete)).scalars().all()
diff --git a/apps/backend/app/repositories/site.py b/apps/backend/app/repositories/site.py
new file mode 100644
index 0000000..cd36329
--- /dev/null
+++ b/apps/backend/app/repositories/site.py
@@ -0,0 +1,15 @@
+from collections.abc import Sequence
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Site
+
+
+class SiteRepository:
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    async def list_all(self) -> Sequence[Site]:
+        requete = select(Site).order_by(Site.site_id)
+        return (await self._session.execute(requete)).scalars().all()
diff --git a/apps/backend/app/schemas/stats.py b/apps/backend/app/schemas/stats.py
new file mode 100644
index 0000000..b119d50
--- /dev/null
+++ b/apps/backend/app/schemas/stats.py
@@ -0,0 +1,26 @@
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, ConfigDict
+
+
+class SiteSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    site_id: str
+    site_name: str
+    current_consumption_kw: float | None
+    capacity_kw: float
+    load_percent: float | None
+    data_quality: Literal["good", "partial", "degraded", "critical"]
+
+
+class StatsSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    timestamp: datetime
+    total_sites: int
+    total_consumption_kw: float
+    total_capacity_kw: float
+    average_load_percent: float
+    sites: list[SiteSummaryResponse]
diff --git a/apps/backend/app/services/stats.py b/apps/backend/app/services/stats.py
new file mode 100644
index 0000000..c98eace
--- /dev/null
+++ b/apps/backend/app/services/stats.py
@@ -0,0 +1,81 @@
+from dataclasses import dataclass
+from datetime import UTC, datetime
+from typing import Literal
+
+from app.models.energy import Reading, Site
+from app.repositories.reading import ReadingRepository
+from app.repositories.site import SiteRepository
+
+DataQuality = Literal["good", "partial", "degraded", "critical"]
+
+QUALITES_CONNUES: frozenset[str] = frozenset({"good", "partial", "degraded", "critical"})
+
+
+@dataclass(frozen=True, slots=True)
+class SiteConsumption:
+    site_id: str
+    site_name: str
+    current_consumption_kw: float | None
+    capacity_kw: float
+    load_percent: float | None
+    data_quality: DataQuality
+
+
+@dataclass(frozen=True, slots=True)
+class ConsumptionSummary:
+    timestamp: datetime
+    total_sites: int
+    total_consumption_kw: float
+    total_capacity_kw: float
+    average_load_percent: float
+    sites: list[SiteConsumption]
+
+
+class StatsService:
+    def __init__(self, sites: SiteRepository, readings: ReadingRepository) -> None:
+        self._sites = sites
+        self._readings = readings
+
+    async def summary(self) -> ConsumptionSummary:
+        sites = await self._sites.list_all()
+        dernieres = {lecture.site_id: lecture for lecture in await self._readings.latest_by_site()}
+
+        resumes = [self._resume_site(site, dernieres.get(site.site_id)) for site in sites]
+        consommation_totale = sum(r.current_consumption_kw or 0 for r in resumes)
+        capacite_totale = sum(r.capacity_kw for r in resumes)
+
+        return ConsumptionSummary(
+            timestamp=datetime.now(UTC),
+            total_sites=len(resumes),
+            total_consumption_kw=consommation_totale,
+            total_capacity_kw=capacite_totale,
+            average_load_percent=(
+                consommation_totale / capacite_totale * 100 if capacite_totale > 0 else 0
+            ),
+            sites=resumes,
+        )
+
+    @staticmethod
+    def _resume_site(site: Site, derniere: Reading | None) -> SiteConsumption:
+        capacite = site.capacity_kw or 0
+        # Piège : `data_quality` est nul dès qu'un site n'a jamais reçu de lecture, ou que le
+        # producteur n'a pas su la qualifier. Le contrat frontend n'a pas de valeur pour ce cas,
+        # `critical` est la seule des quatre qui n'induit pas une confiance qu'on n'a pas.
+        qualite: DataQuality = "critical"
+        consommation = None
+        if derniere is not None and derniere.data_quality in QUALITES_CONNUES:
+            qualite = derniere.data_quality  # type: ignore[assignment]
+            consommation = derniere.consumption_kw
+
+        charge = (
+            consommation / capacite * 100 if consommation is not None and capacite > 0 else None
+        )
+
+        return SiteConsumption(
+            site_id=site.site_id,
+            site_name=site.site_name,
+            current_consumption_kw=consommation,
+            capacity_kw=capacite,
+            load_percent=charge,
+            data_quality=qualite,
+        )
diff --git a/apps/backend/tests/api/test_stats.py b/apps/backend/tests/api/test_stats.py
new file mode 100644
index 0000000..8e4c439
--- /dev/null
+++ b/apps/backend/tests/api/test_stats.py
@@ -0,0 +1,73 @@
+from collections.abc import Callable, Iterator
+from datetime import UTC, datetime
+from uuid import uuid4
+
+import pytest
+from fastapi import FastAPI
+from httpx import AsyncClient
+
+from app.api.deps import get_current_principal, get_stats_service
+from app.core.principal import Principal
+from app.core.roles import AccountKind, Role
+from app.services.stats import ConsumptionSummary, SiteConsumption
+
+
+def principal(role: Role = Role.LECTEUR) -> Principal:
+    return Principal(
+        id=uuid4(),
+        email=f"{role.value}@enervision.fr",
+        role=role,
+        kind=AccountKind.HUMAIN,
+        must_change_password=False,
+    )
+
+
+class FauxService:
+    def __init__(self) -> None:
+        self.resume = ConsumptionSummary(
+            timestamp=datetime.now(UTC),
+            total_sites=1,
+            total_consumption_kw=87.34,
+            total_capacity_kw=200,
+            average_load_percent=43.7,
+            sites=[
+                SiteConsumption(
+                    site_id="SITE001",
+                    site_name="Bureau Paris La Défense",
+                    current_consumption_kw=87.34,
+                    capacity_kw=200,
+                    load_percent=43.7,
+                    data_quality="good",
+                )
+            ],
+        )
+
+    async def summary(self) -> ConsumptionSummary:
+        return self.resume
+
+
+@pytest.fixture
+def servi(app: FastAPI) -> Iterator[Callable[[], FauxService]]:
+    def installe() -> FauxService:
+        service = FauxService()
+        app.dependency_overrides[get_stats_service] = lambda: service
+        app.dependency_overrides[get_current_principal] = lambda: principal()
+        return service
+
+    yield installe
+    app.dependency_overrides.pop(get_stats_service, None)
+    app.dependency_overrides.pop(get_current_principal, None)
+
+
+async def test_get_summary_returns_the_service_result(
+    servi: Callable[[], FauxService], client: AsyncClient
+) -> None:
+    servi()
+
+    response = await client.get("/api/v1/stats/summary")
+
+    assert response.status_code == 200
+    corps = response.json()
+    assert corps["total_sites"] == 1
+    assert corps["sites"][0]["site_id"] == "SITE001"
+    assert corps["sites"][0]["data_quality"] == "good"
diff --git a/apps/backend/tests/repositories/test_reading.py b/apps/backend/tests/repositories/test_reading.py
new file mode 100644
index 0000000..650d49a
--- /dev/null
+++ b/apps/backend/tests/repositories/test_reading.py
@@ -0,0 +1,72 @@
+import uuid
+from datetime import UTC, datetime, timedelta
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Reading, Site
+from app.repositories.reading import ReadingRepository
+
+pytestmark = pytest.mark.integration
+
+
+def identifiant() -> str:
+    return f"SITE-{uuid.uuid4().hex[:8]}"
+
+
+def lecture(site_id: str, *, timestamp: datetime, consumption_kw: float) -> Reading:
+    return Reading(
+        site_id=site_id,
+        timestamp=timestamp,
+        source="api_current",
+        consumption_kw=consumption_kw,
+        data_quality="good",
+        raw_data={},
+    )
+
+
+async def test_latest_by_site_keeps_only_the_most_recent_reading(session: AsyncSession) -> None:
+    site_id = identifiant()
+    maintenant = datetime.now(UTC)
+    session.add(Site(site_id=site_id, site_name="Site", site_type="bureau", capacity_kw=100))
+    await session.flush()
+    session.add_all(
+        [
+            lecture(site_id, timestamp=maintenant - timedelta(hours=1), consumption_kw=10),
+            lecture(site_id, timestamp=maintenant, consumption_kw=42),
+        ]
+    )
+    await session.flush()
+    depot = ReadingRepository(session)
+
+    resultats = await depot.latest_by_site()
+    consommations = [r.consumption_kw for r in resultats if r.site_id == site_id]
+    await session.rollback()
+
+    assert consommations == [42]
+
+
+async def test_latest_by_site_returns_one_row_per_site(session: AsyncSession) -> None:
+    premier, second = identifiant(), identifiant()
+    maintenant = datetime.now(UTC)
+    session.add_all(
+        [
+            Site(site_id=premier, site_name="A", site_type="bureau", capacity_kw=100),
+            Site(site_id=second, site_name="B", site_type="bureau", capacity_kw=200),
+        ]
+    )
+    await session.flush()
+    session.add_all(
+        [
+            lecture(premier, timestamp=maintenant, consumption_kw=10),
+            lecture(second, timestamp=maintenant, consumption_kw=20),
+        ]
+    )
+    await session.flush()
+    depot = ReadingRepository(session)
+
+    resultats = await depot.latest_by_site()
+    identifiants = {r.site_id for r in resultats if r.site_id in (premier, second)}
+    await session.rollback()
+
+    assert identifiants == {premier, second}
diff --git a/apps/backend/tests/repositories/test_site.py b/apps/backend/tests/repositories/test_site.py
new file mode 100644
index 0000000..499e808
--- /dev/null
+++ b/apps/backend/tests/repositories/test_site.py
@@ -0,0 +1,31 @@
+import uuid
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Site
+from app.repositories.site import SiteRepository
+
+pytestmark = pytest.mark.integration
+
+
+def identifiant() -> str:
+    return f"SITE-{uuid.uuid4().hex[:8]}"
+
+
+async def test_list_all_returns_every_site_sorted_by_id(session: AsyncSession) -> None:
+    premier, second = sorted([identifiant(), identifiant()])
+    session.add_all(
+        [
+            Site(site_id=second, site_name="B", site_type="bureau", capacity_kw=100),
+            Site(site_id=premier, site_name="A", site_type="bureau", capacity_kw=50),
+        ]
+    )
+    await session.flush()
+    depot = SiteRepository(session)
+
+    sites = await depot.list_all()
+    identifiants = [site.site_id for site in sites if site.site_id in (premier, second)]
+    await session.rollback()
+
+    assert identifiants == [premier, second]
diff --git a/apps/backend/tests/services/test_stats.py b/apps/backend/tests/services/test_stats.py
new file mode 100644
index 0000000..1962678
--- /dev/null
+++ b/apps/backend/tests/services/test_stats.py
@@ -0,0 +1,107 @@
+from dataclasses import dataclass
+
+from app.services.stats import StatsService
+
+
+@dataclass
+class FauxSite:
+    site_id: str
+    site_name: str
+    capacity_kw: float | None
+
+
+@dataclass
+class FauxLecture:
+    site_id: str
+    consumption_kw: float | None
+    data_quality: str | None
+
+
+class FauxDepotSites:
+    def __init__(self, sites: list[FauxSite]) -> None:
+        self._sites = sites
+
+    async def list_all(self) -> list[FauxSite]:
+        return self._sites
+
+
+class FauxDepotLectures:
+    def __init__(self, lectures: list[FauxLecture]) -> None:
+        self._lectures = lectures
+
+    async def latest_by_site(self) -> list[FauxLecture]:
+        return self._lectures
+
+
+async def test_summary_computes_totals_and_the_average_load() -> None:
+    service = StatsService(
+        sites=FauxDepotSites([FauxSite("A", "Site A", 200), FauxSite("B", "Site B", 800)]),  # type: ignore[arg-type]
+        readings=FauxDepotLectures(  # type: ignore[arg-type]
+            [
+                FauxLecture("A", 100, "good"),
+                FauxLecture("B", 400, "good"),
+            ]
+        ),
+    )
+
+    resume = await service.summary()
+
+    assert resume.total_sites == 2
+    assert resume.total_consumption_kw == 500
+    assert resume.total_capacity_kw == 1000
+    assert resume.average_load_percent == 50
+    par_site = {site.site_id: site for site in resume.sites}
+    assert par_site["A"].load_percent == 50
+    assert par_site["B"].load_percent == 50
+
+
+async def test_summary_treats_a_site_without_any_reading_as_critical() -> None:
+    service = StatsService(
+        sites=FauxDepotSites([FauxSite("A", "Site A", 200)]),  # type: ignore[arg-type]
+        readings=FauxDepotLectures([]),  # type: ignore[arg-type]
+    )
+
+    resume = await service.summary()
+
+    site = resume.sites[0]
+    assert site.data_quality == "critical"
+    assert site.current_consumption_kw is None
+    assert site.load_percent is None
+
+
+async def test_summary_treats_a_reading_with_an_unknown_quality_as_critical() -> None:
+    service = StatsService(
+        sites=FauxDepotSites([FauxSite("A", "Site A", 200)]),  # type: ignore[arg-type]
+        readings=FauxDepotLectures([FauxLecture("A", 50, None)]),  # type: ignore[arg-type]
+    )
+
+    resume = await service.summary()
+
+    site = resume.sites[0]
+    assert site.data_quality == "critical"
+    assert site.current_consumption_kw is None
+
+
+async def test_summary_exposes_a_missing_capacity_as_zero_without_dividing_by_it() -> None:
+    service = StatsService(
+        sites=FauxDepotSites([FauxSite("A", "Site A", None)]),  # type: ignore[arg-type]
+        readings=FauxDepotLectures([FauxLecture("A", 50, "good")]),  # type: ignore[arg-type]
+    )
+
+    resume = await service.summary()
+
+    site = resume.sites[0]
+    assert site.capacity_kw == 0
+    assert site.current_consumption_kw == 50
+    assert site.load_percent is None
+
+
+async def test_summary_returns_zero_average_load_when_no_site_has_a_capacity() -> None:
+    service = StatsService(
+        sites=FauxDepotSites([FauxSite("A", "Site A", None)]),  # type: ignore[arg-type]
+        readings=FauxDepotLectures([]),  # type: ignore[arg-type]
+    )
+
+    resume = await service.summary()
+
+    assert resume.average_load_percent == 0
diff --git a/docs/architecture/20-backend.md b/docs/architecture/20-backend.md
index 8688a6a..d361323 100644
--- a/docs/architecture/20-backend.md
+++ b/docs/architecture/20-backend.md
@@ -12,11 +12,11 @@ Les quatre couches existent désormais, portées par l'authentification.
 
 ```mermaid
 flowchart TB
-  ep["endpoints<br/>health, auth, users"]
+  ep["endpoints<br/>health, auth, users, stats"]
   sc["schemas<br/>Pydantic"]
-  sv["services<br/>AuthService, UserService"]
-  rp["repositories<br/>user, refresh_token,<br/>login_attempt, audit_log"]
-  md["models<br/>4 tables"]
+  sv["services<br/>AuthService, UserService, StatsService"]
+  rp["repositories<br/>user, refresh_token,<br/>login_attempt, audit_log,<br/>site, reading"]
+  md["models<br/>6 tables"]
   db[("PostgreSQL")]
 
   ep --> sc
@@ -140,6 +140,7 @@ Deux fichiers d'environnement, deux usages : `.env` à la racine alimente `docke
 | POST | `/api/v1/users` | oui | Crée un compte, rend un mot de passe provisoire. `admin` |
 | PATCH | `/api/v1/users/{id}` | oui | Change le rôle ou l'activation. `admin` |
 | POST | `/api/v1/users/{id}/password-reset` | oui | Réinitialise et ferme les sessions. `admin` |
+| GET | `/api/v1/stats/summary` | oui | Résume la consommation instantanée du parc. `lecteur` |
 | GET | `/metrics` | non | Format Prometheus. Jeton requis si `APP_METRICS_TOKEN` est posé |
 | GET | `/docs`, `/redoc`, `/openapi.json` | non | Fermés en `staging` et en `prod` |
 
@@ -148,7 +149,7 @@ Deux fichiers d'environnement, deux usages : `.env` à la racine alimente `docke
 échoue si l'une d'elles répond autre chose qu'un 401 ou un 403. Rendre une route publique impose
 donc de modifier la liste dans ce fichier de test.
 
-Aucune route métier n'existe à ce jour. Le contrat détaillé pour le frontend est dans
+Le contrat détaillé pour le frontend est dans
 [31-contrat-authentification.md](31-contrat-authentification.md).
 
 ### `/health/ready`