diff --git a/cmd/buildkitd/config/gcpolicy.go b/cmd/buildkitd/config/gcpolicy.go
index 4078cc6d5910e..2e63da2267643 100644
--- a/cmd/buildkitd/config/gcpolicy.go
+++ b/cmd/buildkitd/config/gcpolicy.go
@@ -104,3 +104,20 @@ func stripQuotes(s string) string {
 	}
 	return s
 }
+
+func DetectDefaultGCCap() DiskSpace {
+	return DiskSpace{Percentage: DiskSpacePercentage}
+}
+
+func (d DiskSpace) AsBytes(root string) int64 {
+	if d.Bytes != 0 {
+		return d.Bytes
+	}
+	if d.Percentage == 0 {
+		return 0
+	}
+
+	avail := getDiskSize(root) * d.Percentage / 100
+	rounded := (avail/(1<<30) + 1) * 1e9 // round up
+	return rounded
+}
diff --git a/cmd/buildkitd/config/gcpolicy_unix.go b/cmd/buildkitd/config/gcpolicy_unix.go
index 232a9ac336cfe..b1af6071cf4ff 100644
--- a/cmd/buildkitd/config/gcpolicy_unix.go
+++ b/cmd/buildkitd/config/gcpolicy_unix.go
@@ -5,25 +5,18 @@ package config
 
 import (
 	"syscall"
-)
 
-func DetectDefaultGCCap() DiskSpace {
-	return DiskSpace{Percentage: 10}
-}
+	"github.com/moby/buildkit/util/bklog"
+)
 
-func (d DiskSpace) AsBytes(root string) int64 {
-	if d.Bytes != 0 {
-		return d.Bytes
-	}
-	if d.Percentage == 0 {
-		return 0
-	}
+var DiskSpacePercentage int64 = 10
 
+func getDiskSize(root string) int64 {
 	var st syscall.Statfs_t
 	if err := syscall.Statfs(root, &st); err != nil {
+		bklog.L.Warnf("failed to get disk size: %v", err)
 		return defaultCap
 	}
 	diskSize := int64(st.Bsize) * int64(st.Blocks)
-	avail := diskSize * d.Percentage / 100
-	return (avail/(1<<30) + 1) * 1e9 // round up
+	return diskSize
 }
diff --git a/cmd/buildkitd/config/gcpolicy_windows.go b/cmd/buildkitd/config/gcpolicy_windows.go
index 55ce4dd77278c..229f500d4a366 100644
--- a/cmd/buildkitd/config/gcpolicy_windows.go
+++ b/cmd/buildkitd/config/gcpolicy_windows.go
@@ -3,10 +3,32 @@
 
 package config
 
-func DetectDefaultGCCap() DiskSpace {
-	return DiskSpace{Bytes: defaultCap}
-}
+import (
+	"github.com/moby/buildkit/util/bklog"
+	"golang.org/x/sys/windows"
+)
+
+// set as double that for Linux since
+// Windows images are generally larger.
+var DiskSpacePercentage int64 = 20
+
+func getDiskSize(root string) int64 {
+	rootUTF16, err := windows.UTF16FromString(root)
+	if err != nil {
+		bklog.L.Warnf("failed to convert root dir to UTF16: %v", err)
+		return defaultCap
+	}
+	var freeAvailableBytes uint64
+	var totalBytes uint64
+	var totalFreeBytes uint64
 
-func (d DiskSpace) AsBytes(root string) int64 {
-	return d.Bytes
+	if err := windows.GetDiskFreeSpaceEx(
+		&rootUTF16[0],
+		&freeAvailableBytes,
+		&totalBytes,
+		&totalFreeBytes); err != nil {
+		bklog.L.Warnf("failed to get disk size: %v", err)
+		return defaultCap
+	}
+	return int64(totalBytes)
 }