diff --git a/weed/worker/tasks/erasure_coding/detection.go b/weed/worker/tasks/erasure_coding/detection.go
index 1122d2721..b40298f81 100644
--- a/weed/worker/tasks/erasure_coding/detection.go
+++ b/weed/worker/tasks/erasure_coding/detection.go
@@ -61,15 +61,16 @@ func Detection(metrics []*types.VolumeHealthMetrics, clusterInfo *types.ClusterI
 
 		// Check quiet duration and fullness criteria
 		if metric.Age >= quietThreshold && metric.FullnessRatio >= ecConfig.FullnessRatio {
+			expectedShardSize := calculateExpectedShardSize(metric.Size)
 			result := &types.TaskDetectionResult{
 				TaskType:   types.TaskTypeErasureCoding,
 				VolumeID:   metric.VolumeID,
 				Server:     metric.Server,
 				Collection: metric.Collection,
 				Priority:   types.TaskPriorityLow, // EC is not urgent
-				Reason: fmt.Sprintf("Volume meets EC criteria: quiet for %.1fs (>%ds), fullness=%.1f%% (>%.1f%%), size=%.1fMB (>%dMB)",
+				Reason: fmt.Sprintf("Volume meets EC criteria: quiet for %.1fs (>%ds), fullness=%.1f%% (>%.1f%%), size=%.1fMB (>%dMB), expected shard size=%.1fMB",
 					metric.Age.Seconds(), ecConfig.QuietForSeconds, metric.FullnessRatio*100, ecConfig.FullnessRatio*100,
-					float64(metric.Size)/(1024*1024), ecConfig.MinSizeMB),
+					float64(metric.Size)/(1024*1024), ecConfig.MinSizeMB, float64(expectedShardSize)/(1024*1024)),
 				ScheduleAt: now,
 			}
 
@@ -97,8 +98,8 @@ func Detection(metrics []*types.VolumeHealthMetrics, clusterInfo *types.ClusterI
 					},
 				}
 
-				glog.V(1).Infof("Planned EC destinations for volume %d: %d shards across %d racks, %d DCs",
-					metric.VolumeID, len(multiPlan.Plans), multiPlan.SuccessfulRack, multiPlan.SuccessfulDCs)
+				glog.V(1).Infof("Planned EC destinations for volume %d: %d shards across %d racks, %d DCs, expected shard size: %.2fMB",
+					metric.VolumeID, len(multiPlan.Plans), multiPlan.SuccessfulRack, multiPlan.SuccessfulDCs, float64(expectedShardSize)/(1024*1024))
 			} else {
 				glog.Warningf("No ActiveTopology available for destination planning in EC detection")
 				continue // Skip this volume if no topology available
@@ -143,6 +144,10 @@ func Detection(metrics []*types.VolumeHealthMetrics, clusterInfo *types.ClusterI
 // planECDestinations plans the destinations for erasure coding operation
 // This function implements EC destination planning logic directly in the detection phase
 func planECDestinations(activeTopology *topology.ActiveTopology, metric *types.VolumeHealthMetrics, ecConfig *Config) (*topology.MultiDestinationPlan, error) {
+	// Calculate expected shard size based on original volume size
+	// EC data is split across data shards, so each shard gets roughly volume_size / data_shards
+	expectedShardSize := calculateExpectedShardSize(metric.Size)
+
 	// Get source node information from topology
 	var sourceRack, sourceDC string
 
@@ -178,9 +183,9 @@ func planECDestinations(activeTopology *topology.ActiveTopology, metric *types.V
 	}
 
 	// Select best disks for EC placement with rack/DC diversity
-	selectedDisks := selectBestECDestinations(availableDisks, sourceRack, sourceDC, erasure_coding.TotalShardsCount)
-	if len(selectedDisks) < minTotalDisks {
-		return nil, fmt.Errorf("found %d disks, but could not find %d suitable destinations for EC placement", len(selectedDisks), minTotalDisks)
+	selectedDisks := selectBestECDestinations(availableDisks, sourceRack, sourceDC, erasure_coding.TotalShardsCount, expectedShardSize)
+	if len(selectedDisks) < erasure_coding.MinTotalDisks {
+		return nil, fmt.Errorf("found %d disks, but could not find %d suitable destinations for EC placement", len(selectedDisks), erasure_coding.MinTotalDisks)
 	}
 
 	var plans []*topology.DestinationPlan
@@ -193,8 +198,8 @@ func planECDestinations(activeTopology *topology.ActiveTopology, metric *types.V
 			TargetDisk:     disk.DiskID,
 			TargetRack:     disk.Rack,
 			TargetDC:       disk.DataCenter,
-			ExpectedSize:   0, // EC shards don't have predetermined size
-			PlacementScore: calculateECScore(disk, sourceRack, sourceDC),
+			ExpectedSize:   expectedShardSize, // Use calculated shard size
+			PlacementScore: calculateECScoreWithSize(disk, sourceRack, sourceDC, expectedShardSize),
 			Conflicts:      checkECPlacementConflicts(disk, sourceRack, sourceDC),
 		}
 		plans = append(plans, plan)
@@ -205,6 +210,9 @@ func planECDestinations(activeTopology *topology.ActiveTopology, metric *types.V
 		dcCount[disk.DataCenter]++
 	}
 
+	glog.V(1).Infof("Planned EC destinations for volume %d (size=%d bytes): expected shard size=%d bytes, %d shards across %d racks, %d DCs",
+		metric.VolumeID, metric.Size, expectedShardSize, len(plans), len(rackCount), len(dcCount))
+
 	return &topology.MultiDestinationPlan{
 		Plans:          plans,
 		TotalShards:    len(plans),
@@ -243,7 +251,7 @@ func createECTaskParams(multiPlan *topology.MultiDestinationPlan) *worker_pb.Era
 }
 
 // selectBestECDestinations selects multiple disks for EC shard placement with diversity
-func selectBestECDestinations(disks []*topology.DiskInfo, sourceRack, sourceDC string, shardsNeeded int) []*topology.DiskInfo {
+func selectBestECDestinations(disks []*topology.DiskInfo, sourceRack, sourceDC string, shardsNeeded int, expectedShardSize uint64) []*topology.DiskInfo {
 	if len(disks) == 0 {
 		return nil
 	}
@@ -265,7 +273,7 @@ func selectBestECDestinations(disks []*topology.DiskInfo, sourceRack, sourceDC s
 		}
 
 		// Select best disk from this rack
-		bestDisk := selectBestFromRack(rackDisks, sourceRack, sourceDC)
+		bestDisk := selectBestFromRack(rackDisks, sourceRack, sourceDC, expectedShardSize)
 		if bestDisk != nil {
 			selected = append(selected, bestDisk)
 			usedRacks[rackKey] = true
@@ -298,7 +306,7 @@ func selectBestECDestinations(disks []*topology.DiskInfo, sourceRack, sourceDC s
 }
 
 // selectBestFromRack selects the best disk from a rack for EC placement
-func selectBestFromRack(disks []*topology.DiskInfo, sourceRack, sourceDC string) *topology.DiskInfo {
+func selectBestFromRack(disks []*topology.DiskInfo, sourceRack, sourceDC string, expectedShardSize uint64) *topology.DiskInfo {
 	if len(disks) == 0 {
 		return nil
 	}
@@ -311,7 +319,7 @@ func selectBestFromRack(disks []*topology.DiskInfo, sourceRack, sourceDC string)
 			continue
 		}
 
-		score := calculateECScore(disk, sourceRack, sourceDC)
+		score := calculateECScoreWithSize(disk, sourceRack, sourceDC, expectedShardSize)
 		if score > bestScore {
 			bestScore = score
 			bestDisk = disk
@@ -351,6 +359,24 @@ func calculateECScore(disk *topology.DiskInfo, sourceRack, sourceDC string) floa
 	return score
 }
 
+// calculateECScoreWithSize calculates placement score for EC operations with shard size consideration
+func calculateECScoreWithSize(disk *topology.DiskInfo, sourceRack, sourceDC string, expectedShardSize uint64) float64 {
+	baseScore := calculateECScore(disk, sourceRack, sourceDC)
+
+	// Additional scoring based on available space vs expected shard size
+	if disk.DiskInfo != nil && expectedShardSize > 0 {
+		// Estimate available space (this is a rough estimate)
+		availableSlots := disk.DiskInfo.MaxVolumeCount - disk.DiskInfo.VolumeCount
+		if availableSlots > 0 {
+			// Bonus for having plenty of space for the expected shard
+			// This is a heuristic - each volume slot can theoretically hold any size
+			baseScore += float64(availableSlots) * 2.0 // Up to 2 points per available slot
+		}
+	}
+
+	return baseScore
+}
+
 // isDiskSuitableForEC checks if a disk is suitable for EC placement
 func isDiskSuitableForEC(disk *topology.DiskInfo) bool {
 	if disk.DiskInfo == nil {
@@ -414,3 +440,23 @@ func findVolumeReplicas(activeTopology *topology.ActiveTopology, volumeID uint32
 
 	return replicaServers
 }
+
+// calculateExpectedShardSize calculates the expected size of each EC shard based on the original volume size
+func calculateExpectedShardSize(originalVolumeSize uint64) uint64 {
+	if originalVolumeSize == 0 {
+		return 0
+	}
+
+	// In erasure coding, the original data is split across data shards
+	// Each data shard gets approximately originalSize / dataShards
+	// Parity shards are similar in size to data shards
+	// Add some overhead for padding and metadata (typically ~5-10%)
+	baseShardSize := originalVolumeSize / uint64(erasure_coding.DataShardsCount)
+	overhead := baseShardSize / 10 // 10% overhead for padding and metadata
+	expectedShardSize := baseShardSize + overhead
+
+	glog.V(2).Infof("Calculated expected shard size: original=%d bytes, base_shard=%d bytes, with_overhead=%d bytes",
+		originalVolumeSize, baseShardSize, expectedShardSize)
+
+	return expectedShardSize
+}