diff --git a/lfs3.c b/lfs3.c
index 327ed0cd..96f7d6a2 100644
--- a/lfs3.c
+++ b/lfs3.c
@@ -10459,6 +10459,8 @@ eot:;
 static void lfs3_gbmap_init(lfs3_gbmap_t *gbmap) {
     gbmap->window = 0;
     gbmap->known = 0;
+    // we lazily populate this during lookahead scans
+    gbmap->known_free = -1;
     lfs3_btree_init(&gbmap->b);
     lfs3_btree_init(&gbmap->b_p);
 }
@@ -16069,6 +16071,7 @@ failed:;
 
 /// Other filesystem things  ///
 
+// note lfs3_fs_stat should never go to disk
 int lfs3_fs_stat(lfs3_t *lfs3, struct lfs3_fsinfo *fsinfo) {
     // return various filesystem flags
     fsinfo->flags = lfs3->flags & (
@@ -16099,6 +16102,34 @@ int lfs3_fs_stat(lfs3_t *lfs3, struct lfs3_fsinfo *fsinfo) {
     fsinfo->name_limit = lfs3->name_limit;
     fsinfo->file_limit = lfs3->file_limit;
 
+    // return best effort knowledge of block usage
+
+    // if we have a gbmap, we choose whichever allocator has more
+    // information, otherwise we fall back to the lookahead buffer
+    if (LFS3_IFDEF_GBMAP(
+            lfs3_f_isgbmap(lfs3->flags)
+                // known_free=-1 indicates we don't know the free/inuse
+                // breakdown yet
+                && lfs3->gbmap.known_free != -1
+                && lfs3->gbmap.known >= lfs3->lookahead.known,
+            false)) {
+        #ifdef LFS3_GBMAP
+        fsinfo->known_free = lfs3->gbmap.known_free;
+        fsinfo->known_inuse = lfs3->gbmap.known - lfs3->gbmap.known_free;
+        #endif
+
+    } else {
+        lfs3_block_t free = 0;
+        for (lfs3_size_t i = 0; i < lfs3->lookahead.known; i++) {
+            if (!(lfs3->lookahead.buffer[(lfs3->lookahead.off+i) / 8]
+                    & (1 << ((lfs3->lookahead.off+i) % 8)))) {
+                free += 1;
+            }
+        }
+        fsinfo->known_free = free;
+        fsinfo->known_inuse = lfs3->lookahead.known - free;
+    }
+
     return 0;
 }
 
diff --git a/lfs3.h b/lfs3.h
index b007612d..59d9654a 100644
--- a/lfs3.h
+++ b/lfs3.h
@@ -687,6 +687,16 @@ struct lfs3_fsinfo {
 
     // Upper limit on the size of files in bytes.
     lfs3_off_t file_limit;
+
+    // Number of known free blocks
+    //
+    // Note this is limited by lookahead/gbmap
+    lfs3_block_t known_free;
+
+    // Number of known in-use blocks
+    //
+    // Note this is limited by lookahead/gbmap
+    lfs3_block_t known_inuse;
 };
 
 // Traversal info structure
@@ -1221,6 +1231,7 @@ typedef struct lfs3_grm {
 typedef struct lfs3_gbmap {
     lfs3_block_t window;
     lfs3_block_t known;
+    lfs3_sblock_t known_free;
     lfs3_btree_t b;
     lfs3_btree_t b_p;
 } lfs3_gbmap_t;
@@ -1276,7 +1287,7 @@ typedef struct lfs3 {
     struct lfs3_lookahead {
         lfs3_block_t window;
         lfs3_block_t off;
-        lfs3_block_t known;
+        lfs3_size_t known;
         lfs3_block_t ckpoint;
         uint8_t *buffer;
     } lookahead;