diff --git a/cmd/metal-api/internal/service/partition-service.go b/cmd/metal-api/internal/service/partition-service.go
index 09a1bc389..b5fcfbe64 100644
--- a/cmd/metal-api/internal/service/partition-service.go
+++ b/cmd/metal-api/internal/service/partition-service.go
@@ -433,7 +433,7 @@ func (r *partitionResource) calcPartitionCapacity(pcr *v1.PartitionCapacityReque
 				reservation := reservation
 
 				cap.Reservations += reservation.Amount
-				cap.UnusedReservations += max(reservation.Amount-len(machinesByProject[reservation.ProjectID]), 0)
+				cap.UsedReservations += len(machinesByProject[reservation.ProjectID])
 			}
 		}
 
diff --git a/cmd/metal-api/internal/service/partition-service_test.go b/cmd/metal-api/internal/service/partition-service_test.go
index 5a370a120..2ac060d60 100644
--- a/cmd/metal-api/internal/service/partition-service_test.go
+++ b/cmd/metal-api/internal/service/partition-service_test.go
@@ -289,5 +289,5 @@ func TestPartitionCapacity(t *testing.T) {
 	require.Equal(t, 5, c.Total)
 	require.Equal(t, 0, c.Free)
 	require.Equal(t, 0, c.Reservations)
-	require.Equal(t, 0, c.UnusedReservations)
+	require.Equal(t, 0, c.UsedReservations)
 }
diff --git a/cmd/metal-api/internal/service/v1/partition.go b/cmd/metal-api/internal/service/v1/partition.go
index 908b150f2..7bea44237 100644
--- a/cmd/metal-api/internal/service/v1/partition.go
+++ b/cmd/metal-api/internal/service/v1/partition.go
@@ -47,16 +47,16 @@ type PartitionCapacity struct {
 }
 
 type ServerCapacity struct {
-	Size               string   `json:"size" description:"the size of the server"`
-	Total              int      `json:"total" description:"total amount of servers with this size"`
-	Free               int      `json:"free" description:"free servers with this size"`
-	Allocated          int      `json:"allocated" description:"allocated servers with this size"`
-	Reservations       int      `json:"reservations" description:"the amount of reservations for this size"`
-	UnusedReservations int      `json:"unusedreservations" description:"the amount of unused reservations for this size"`
-	Faulty             int      `json:"faulty" description:"servers with issues with this size"`
-	FaultyMachines     []string `json:"faultymachines" description:"servers with issues with this size"`
-	Other              int      `json:"other" description:"servers neither free, allocated or faulty with this size"`
-	OtherMachines      []string `json:"othermachines" description:"servers neither free, allocated or faulty with this size"`
+	Size             string   `json:"size" description:"the size of the server"`
+	Total            int      `json:"total" description:"total amount of servers with this size"`
+	Free             int      `json:"free" description:"free servers with this size"`
+	Allocated        int      `json:"allocated" description:"allocated servers with this size"`
+	Reservations     int      `json:"reservations" description:"the amount of reservations for this size"`
+	UsedReservations int      `json:"usedreservations" description:"the amount of used reservations for this size"`
+	Faulty           int      `json:"faulty" description:"servers with issues with this size"`
+	FaultyMachines   []string `json:"faultymachines" description:"servers with issues with this size"`
+	Other            int      `json:"other" description:"servers neither free, allocated or faulty with this size"`
+	OtherMachines    []string `json:"othermachines" description:"servers neither free, allocated or faulty with this size"`
 }
 
 func NewPartitionResponse(p *metal.Partition) *PartitionResponse {
diff --git a/spec/metal-api.json b/spec/metal-api.json
index 02fe540d2..6310ee36b 100644
--- a/spec/metal-api.json
+++ b/spec/metal-api.json
@@ -4262,8 +4262,8 @@
           "format": "int32",
           "type": "integer"
         },
-        "unusedreservations": {
-          "description": "the amount of unused reservations for this size",
+        "usedreservations": {
+          "description": "the amount of used reservations for this size",
           "format": "int32",
           "type": "integer"
         }
@@ -4278,7 +4278,7 @@
         "reservations",
         "size",
         "total",
-        "unusedreservations"
+        "usedreservations"
       ]
     },
     "v1.SizeConstraint": {