diff --git a/cmd/composectl/cmd/check.go b/cmd/composectl/cmd/check.go
index b32763b..1f1a96a 100644
--- a/cmd/composectl/cmd/check.go
+++ b/cmd/composectl/cmd/check.go
@@ -195,8 +195,15 @@ func checkApps(ctx context.Context,
 			fmt.Println()
 		}
 	}
+	// On a daemon whose images are installed into containerd, the layers to unpack are those without
+	// a snapshot, whether their blobs are in the store or not.
+	unpackSize, onCtrd, err := compose.CtrdUnpackSize(ctx, config, status.Apps, srcBlobProvider)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("failed to size the install into dockerd's containerd: %w", err)
+	}
 	checkResult := &CheckAppResult{
-		MissingBlobs: status.MissingBlobs,
+		MissingBlobs:     status.MissingBlobs,
+		TotalRuntimeSize: unpackSize,
 	}
 	for _, bi := range status.MissingBlobs {
 		if bi.State == compose.BlobFetching {
@@ -206,7 +213,9 @@ func checkApps(ctx context.Context,
 			checkResult.TotalPullSize += bi.Descriptor.Size
 			checkResult.TotalStoreSize += bi.StoreSize
 		}
-		checkResult.TotalRuntimeSize += bi.RuntimeSize
+		if !onCtrd || bi.Type != compose.BlobTypeImageLayer {
+			checkResult.TotalRuntimeSize += bi.RuntimeSize
+		}
 	}
 	ui, err := compose.GetUsageInfo(config.StoreRoot,
 		checkResult.TotalStoreSize+checkResult.TotalRuntimeSize, watermark, watermarkInBytes)
diff --git a/pkg/compose/ctrd_sizing.go b/pkg/compose/ctrd_sizing.go
new file mode 100644
index 0000000..88306d5
--- /dev/null
+++ b/pkg/compose/ctrd_sizing.go
@@ -0,0 +1,81 @@
+package compose
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// CtrdUnpackSize returns the unpacked size of the image layers that installing the apps into
+// dockerd's containerd has to unpack: in each image, the layer of the first missing snapshot and
+// every layer above it. onCtrd is false when the images are loaded with `docker load` instead.
+func CtrdUnpackSize(ctx context.Context, cfg *Config, apps []App, provider BlobProvider) (size int64, onCtrd bool, err error) {
+	c, err := ctrdIfInstallTarget(ctx, cfg)
+	if err != nil || c == nil {
+		return 0, false, err
+	}
+	defer c.Close()
+	size, err = unpackSize(ctx, cfg, apps, provider, c.firstMissingSnapshot)
+	return size, true, err
+}
+
+// unpackSize counts each snapshot once by chain ID across all images; firstMissing returns the
+// index of the first layer of a chain whose snapshot does not exist. An image whose manifest or
+// config cannot be read has no known chain: all its layers are counted, so the size never drops
+// below what the install unpacks.
+func unpackSize(ctx context.Context, cfg *Config, apps []App, provider BlobProvider,
+	firstMissing func(context.Context, []digest.Digest) (int, error)) (int64, error) {
+	var size int64
+	counted := map[digest.Digest]bool{}
+	for _, app := range apps {
+		runtimeSize := func(layer *ocispec.Descriptor) int64 {
+			return app.GetBlobRuntimeSize(layer, cfg.Platform.Architecture, cfg.BlockSize)
+		}
+		for _, root := range app.GetComposeRoot().Children {
+			img, err := ctrdImageOf(ctx, root, provider)
+			if err != nil {
+				size += layersSize(treeLayersOf(root), nil, counted, runtimeSize)
+				continue
+			}
+			first, err := firstMissing(ctx, img.chainIDs)
+			if err != nil {
+				return 0, fmt.Errorf("failed to scan the snapshots of %s: %w", img.ref, err)
+			}
+			size += layersSize(img.layers[first:], img.chainIDs[first:], counted, runtimeSize)
+		}
+	}
+	return size, nil
+}
+
+// layersSize sums the runtime size of the layers whose chain ID is not counted yet; without chain
+// IDs every layer is summed.
+func layersSize(layers []ocispec.Descriptor, chainIDs []digest.Digest, counted map[digest.Digest]bool,
+	runtimeSize func(*ocispec.Descriptor) int64) (size int64) {
+	for i := range layers {
+		if chainIDs != nil && counted[chainIDs[i]] {
+			continue
+		}
+		if chainIDs != nil {
+			counted[chainIDs[i]] = true
+		}
+		size += runtimeSize(&layers[i])
+	}
+	return size
+}
+
+// treeLayersOf returns the layer descriptors the app tree holds for an image.
+func treeLayersOf(root *TreeNode) []ocispec.Descriptor {
+	mNode, err := platformManifestNode(root)
+	if err != nil {
+		return nil
+	}
+	var layers []ocispec.Descriptor
+	for _, child := range mNode.Children {
+		if child.Type == BlobTypeImageLayer {
+			layers = append(layers, *child.Descriptor)
+		}
+	}
+	return layers
+}
diff --git a/pkg/compose/ctrd_sizing_test.go b/pkg/compose/ctrd_sizing_test.go
new file mode 100644
index 0000000..cd786e6
--- /dev/null
+++ b/pkg/compose/ctrd_sizing_test.go
@@ -0,0 +1,139 @@
+package compose
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"testing"
+
+	"github.com/opencontainers/go-digest"
+	"github.com/opencontainers/image-spec/identity"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// sizingApp is an App with a compose root of images whose layers unpack to three times their size.
+type sizingApp struct {
+	App
+	root *TreeNode
+}
+
+func (a *sizingApp) GetComposeRoot() *TreeNode { return a.root }
+
+func (a *sizingApp) GetBlobRuntimeSize(desc *ocispec.Descriptor, _ string, _ int64) int64 {
+	return desc.Size * 3
+}
+
+func sizingLayer(name string, size int64) ocispec.Descriptor {
+	return ocispec.Descriptor{MediaType: ocispec.MediaTypeImageLayerGzip, Digest: digest.FromString(name), Size: size}
+}
+
+func diffID(layer ocispec.Descriptor) digest.Digest {
+	return digest.FromString("diff:" + layer.Digest.String())
+}
+
+// sizingImage puts the manifest and, when withConfig is set, the config of an image into blobs and
+// returns the image's node in the app tree.
+func sizingImage(t *testing.T, blobs map[digest.Digest][]byte, name string, withConfig bool,
+	layers ...ocispec.Descriptor) *TreeNode {
+	t.Helper()
+	var config ocispec.Image
+	for _, l := range layers {
+		config.RootFS.DiffIDs = append(config.RootFS.DiffIDs, diffID(l))
+	}
+	configBytes, err := json.Marshal(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+	configDesc := ocispec.Descriptor{MediaType: ocispec.MediaTypeImageConfig,
+		Digest: digest.FromBytes(configBytes), Size: int64(len(configBytes))}
+	manifestBytes, err := json.Marshal(ocispec.Manifest{Config: configDesc, Layers: layers})
+	if err != nil {
+		t.Fatal(err)
+	}
+	manifestDesc := ocispec.Descriptor{MediaType: ocispec.MediaTypeImageManifest,
+		Digest: digest.FromBytes(manifestBytes), Size: int64(len(manifestBytes))}
+	blobs[manifestDesc.Digest] = manifestBytes
+	if withConfig {
+		blobs[configDesc.Digest] = configBytes
+	}
+	ref := func(d digest.Digest) []string { return []string{"registry.example/factory/" + name + "@" + d.String()} }
+	configDesc.URLs = ref(configDesc.Digest)
+	manifestDesc.URLs = ref(manifestDesc.Digest)
+	node := &TreeNode{Descriptor: &manifestDesc, Type: BlobTypeImageManifest,
+		Children: []*TreeNode{{Descriptor: &configDesc, Type: BlobTypeImageConfig}}}
+	for i := range layers {
+		node.Children = append(node.Children, &TreeNode{Descriptor: &layers[i], Type: BlobTypeImageLayer})
+	}
+	return node
+}
+
+// snapshotsOf is a snapshot lookup in which the snapshots of the given layer chains exist, each
+// with its parents.
+func snapshotsOf(chains ...[]ocispec.Descriptor) func(context.Context, []digest.Digest) (int, error) {
+	exist := map[digest.Digest]bool{}
+	for _, chain := range chains {
+		var diffIDs []digest.Digest
+		for _, l := range chain {
+			diffIDs = append(diffIDs, diffID(l))
+		}
+		for _, id := range identity.ChainIDs(diffIDs) {
+			exist[id] = true
+		}
+	}
+	return func(_ context.Context, chainIDs []digest.Digest) (int, error) {
+		for i, id := range chainIDs {
+			if !exist[id] {
+				return i, nil
+			}
+		}
+		return len(chainIDs), nil
+	}
+}
+
+func TestUnpackSize(t *testing.T) {
+	base, a, b := sizingLayer("base", 100), sizingLayer("a", 10), sizingLayer("b", 20)
+	cfg := &Config{}
+	size := func(withConfig bool, lookup func(context.Context, []digest.Digest) (int, error)) int64 {
+		t.Helper()
+		blobs := map[digest.Digest][]byte{}
+		root := &TreeNode{Children: []*TreeNode{
+			sizingImage(t, blobs, "one", true, base, a),
+			sizingImage(t, blobs, "two", withConfig, base, b),
+		}}
+		got, err := unpackSize(context.Background(), cfg, []App{&sizingApp{root: root}}, NewMemoryBlobProvider(blobs), lookup)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return got
+	}
+
+	// No snapshot exists, as after a prune: every layer, the shared base once.
+	if got := size(true, snapshotsOf()); got != 3*(100+10+20) {
+		t.Errorf("no snapshots: got %d, want %d", got, 3*(100+10+20))
+	}
+	// The base snapshot exists: only the layers above it.
+	if got := size(true, snapshotsOf([]ocispec.Descriptor{base})); got != 3*(10+20) {
+		t.Errorf("base snapshot exists: got %d, want %d", got, 3*(10+20))
+	}
+	// Everything is unpacked already.
+	if got := size(true, snapshotsOf([]ocispec.Descriptor{base, a}, []ocispec.Descriptor{base, b})); got != 0 {
+		t.Errorf("all snapshots exist: got %d, want 0", got)
+	}
+	// The second image has no config in the store: all its layers count, even the shared base.
+	if got := size(false, snapshotsOf([]ocispec.Descriptor{base})); got != 3*(10+100+20) {
+		t.Errorf("unreadable config: got %d, want %d", got, 3*(10+100+20))
+	}
+	if got := size(false, snapshotsOf()); got != 3*(100+10+100+20) {
+		t.Errorf("unreadable config, no snapshots: got %d, want %d", got, 3*(100+10+100+20))
+	}
+}
+
+func TestUnpackSizeFailsOnSnapshotError(t *testing.T) {
+	blobs := map[digest.Digest][]byte{}
+	root := &TreeNode{Children: []*TreeNode{sizingImage(t, blobs, "one", true, sizingLayer("base", 100))}}
+	failing := func(context.Context, []digest.Digest) (int, error) { return 0, errors.New("unavailable") }
+	_, err := unpackSize(context.Background(), &Config{}, []App{&sizingApp{root: root}}, NewMemoryBlobProvider(blobs), failing)
+	if err == nil {
+		t.Fatal("expected the snapshot lookup error")
+	}
+}
diff --git a/test/integration/ctrd_install_test.go b/test/integration/ctrd_install_test.go
index c95d36f..f554e04 100644
--- a/test/integration/ctrd_install_test.go
+++ b/test/integration/ctrd_install_test.go
@@ -611,3 +611,80 @@ func aklitePruneAfterKilledInstall(t *testing.T) {
 		t.Errorf("install leases left after the prune: %+v", leftovers)
 	}
 }
+
+// TestCtrdCheckSizesByMissingSnapshots: `check` sizes the runtime by the snapshots the install
+// still has to create, not by the blobs missing from the store: after a prune every blob is still
+// in the store, yet the layers have to be unpacked again.
+func TestCtrdCheckSizesByMissingSnapshots(t *testing.T) {
+	r := newCtrdRig(t)
+	app := f.NewApp(t, ctrdTestApp)
+	app.Publish(t)
+	app.Pull(t)
+	defer app.Remove(t)
+	app.Install(t)
+	defer app.Uninstall(t)
+
+	runtimeSize := func(when string) int64 {
+		t.Helper()
+		res := akliteCheck(t, app.PublishedUri, "--local")
+		if len(res.FetchCheck.MissingBlobs) != 0 {
+			t.Fatalf("%s: check reports missing blobs: %+v", when, res.FetchCheck.MissingBlobs)
+		}
+		return res.FetchCheck.TotalRuntimeSize
+	}
+	if size := runtimeSize("installed"); size != 0 {
+		t.Fatalf("installed: total_runtime_size is %d, want 0", size)
+	}
+	r.pruneImages(r.topChainIDs(app))
+	if size := runtimeSize("pruned"); size <= 0 {
+		t.Fatalf("pruned: total_runtime_size is %d, want more than 0", size)
+	}
+	app.Install(t)
+	if size := runtimeSize("reinstalled"); size != 0 {
+		t.Fatalf("reinstalled: total_runtime_size is %d, want 0", size)
+	}
+}
+
+// TestCtrdCheckSizesImageWithMissingConfig: `check --local` of an app whose image config is not
+// in the store (an interrupted fetch) reports the missing config and sizes the runtime as if every
+// layer had to be unpacked.
+func TestCtrdCheckSizesImageWithMissingConfig(t *testing.T) {
+	r := newCtrdRig(t)
+	app := f.NewApp(t, ctrdTestApp)
+	app.Publish(t)
+	app.Pull(t)
+	defer app.Remove(t)
+	r.pruneImages(r.topChainIDs(app)) // no snapshot of the app exists: every layer counts
+
+	cfg := f.NewTestConfig(t)
+	tree, err := v1.NewAppLoader().LoadAppTree(context.Background(), compose.NewStoreBlobProvider(r.blobsRoot),
+		platforms.OnlyStrict(cfg.Platform), app.PublishedUri)
+	f.Check(t, err)
+	var unpacked int64
+	seen := map[digest.Digest]bool{}
+	imgs := r.images(app.PublishedUri)
+	for _, img := range imgs {
+		for _, layer := range img.manifest.Layers {
+			if !seen[layer.Digest] {
+				seen[layer.Digest] = true
+				unpacked += tree.GetBlobRuntimeSize(&layer, cfg.Platform.Architecture, cfg.BlockSize)
+			}
+		}
+	}
+
+	configDigest := imgs[0].manifest.Config.Digest
+	configPath := filepath.Join(r.blobsRoot, configDigest.Encoded())
+	config, err := os.ReadFile(configPath)
+	f.Check(t, err)
+	f.Check(t, os.Remove(configPath))
+	defer func() { f.Check(t, os.WriteFile(configPath, config, 0o444)) }()
+
+	res := akliteCheck(t, app.PublishedUri, "--local")
+	if _, ok := res.FetchCheck.MissingBlobs[configDigest]; !ok {
+		t.Errorf("check does not list the config among the missing blobs: %+v", res.FetchCheck.MissingBlobs)
+	}
+	if res.FetchCheck.TotalRuntimeSize < unpacked {
+		t.Errorf("total_runtime_size %d is below the unpacked size of the layers %d",
+			res.FetchCheck.TotalRuntimeSize, unpacked)
+	}
+}