diff --git a/include/xfrog.h b/include/xfrog.h
index 6b605dcf..5748e967 100644
--- a/include/xfrog.h
+++ b/include/xfrog.h
@@ -45,6 +45,9 @@ struct xfs_fd {
 
 	/* bits for agino in inum */
 	unsigned int		aginolog;
+
+	/* log2 of sb_blocksize / sb_sectsize */
+	unsigned int		blkbb_log;
 };
 
 /* Static initializers */
@@ -100,6 +103,69 @@ xfrog_b_to_fsbt(
 	return bytes >> xfd->blocklog;
 }
 
+/* Convert sector number to bytes. */
+static inline uint64_t
+xfrog_bbtob(
+	uint64_t		daddr)
+{
+	return daddr << BBSHIFT;
+}
+
+/* Convert bytes to sector number, rounding down. */
+static inline uint64_t
+xfrog_btobbt(
+	uint64_t		bytes)
+{
+	return bytes >> BBSHIFT;
+}
+
+/* Convert fs block number to sector number. */
+static inline uint64_t
+xfrog_fsb_to_bb(
+	struct xfs_fd		*xfd,
+	uint64_t		fsbno)
+{
+	return fsbno << xfd->blkbb_log;
+}
+
+/* Convert sector number to fs block number, rounded down. */
+static inline uint64_t
+xfrog_bb_to_fsbt(
+	struct xfs_fd		*xfd,
+	uint64_t		daddr)
+{
+	return daddr >> xfd->blkbb_log;
+}
+
+/* Convert AG number and AG block to fs block number */
+static inline uint64_t
+xfrog_agb_to_daddr(
+	struct xfs_fd		*xfd,
+	uint32_t		agno,
+	uint32_t		agbno)
+{
+	return xfrog_fsb_to_bb(xfd,
+			(uint64_t)agno * xfd->fsgeom.agblocks + agbno);
+}
+
+/* Convert sector number to AG number. */
+static inline uint32_t
+xfrog_daddr_to_agno(
+	struct xfs_fd		*xfd,
+	uint64_t		daddr)
+{
+	return xfrog_bb_to_fsbt(xfd, daddr) / xfd->fsgeom.agblocks;
+}
+
+/* Convert sector number to AG block number. */
+static inline uint32_t
+xfrog_daddr_to_agbno(
+	struct xfs_fd		*xfd,
+	uint64_t		daddr)
+{
+	return xfrog_bb_to_fsbt(xfd, daddr) % xfd->fsgeom.agblocks;
+}
+
 /* Bulkstat wrappers */
 struct xfs_bstat;
 int xfrog_bulkstat_single(struct xfs_fd *xfd, uint64_t ino,
diff --git a/libfrog/fsgeom.c b/libfrog/fsgeom.c
index 159738c5..17479e4a 100644
--- a/libfrog/fsgeom.c
+++ b/libfrog/fsgeom.c
@@ -114,6 +114,7 @@ xfrog_prepare_geometry(
 	xfd->inodelog = highbit32(xfd->fsgeom.inodesize);
 	xfd->inopblog = xfd->blocklog - xfd->inodelog;
 	xfd->aginolog = xfd->agblklog + xfd->inopblog;
+	xfd->blkbb_log = xfd->blocklog - BBSHIFT;
 	return 0;
 }
 
diff --git a/spaceman/freesp.c b/spaceman/freesp.c
index 83cbecbd..9e9f32a2 100644
--- a/spaceman/freesp.c
+++ b/spaceman/freesp.c
@@ -150,9 +150,7 @@ scan_ag(
 	struct fsmap		*extent;
 	struct fsmap		*l, *h;
 	struct fsmap		*p;
-	struct xfs_fsop_geom	*fsgeom = &file->xfd.fsgeom;
-	off64_t			blocksize = fsgeom->blocksize;
-	off64_t			bperag;
+	struct xfs_fd		*xfd = &file->xfd;
 	off64_t			aglen;
 	xfs_agblock_t		agbno;
 	unsigned long long	freeblks = 0;
@@ -160,8 +158,6 @@ scan_ag(
 	int			ret;
 	int			i;
 
-	bperag = (off64_t)fsgeom->agblocks * blocksize;
-
 	fsmap = malloc(fsmap_sizeof(NR_EXTENTS));
 	if (!fsmap) {
 		fprintf(stderr, _("%s: fsmap malloc failed.\n"), progname);
@@ -174,8 +170,10 @@ scan_ag(
 	l = fsmap->fmh_keys;
 	h = fsmap->fmh_keys + 1;
 	if (agno != NULLAGNUMBER) {
-		l->fmr_physical = agno * bperag;
-		h->fmr_physical = ((agno + 1) * bperag) - 1;
+		l->fmr_physical = xfrog_bbtob(
+				xfrog_agb_to_daddr(xfd, agno, 0));
+		h->fmr_physical = xfrog_bbtob(
+				xfrog_agb_to_daddr(xfd, agno + 1, 0));
 		l->fmr_device = h->fmr_device = file->fs_path.fs_datadev;
 	} else {
 		l->fmr_physical = 0;
@@ -206,9 +204,9 @@ scan_ag(
 			if (!(extent->fmr_flags & FMR_OF_SPECIAL_OWNER) ||
 			    extent->fmr_owner != XFS_FMR_OWN_FREE)
 				continue;
-			agbno = (extent->fmr_physical - (bperag * agno)) /
-								blocksize;
-			aglen = extent->fmr_length / blocksize;
+			agbno = xfrog_daddr_to_agbno(xfd,
+					xfrog_btobbt(extent->fmr_physical));
+			aglen = xfrog_b_to_fsbt(xfd, extent->fmr_length);
 			freeblks += aglen;
 			freeexts++;
 
diff --git a/spaceman/trim.c b/spaceman/trim.c
index ea1308f7..8741bab2 100644
--- a/spaceman/trim.c
+++ b/spaceman/trim.c
@@ -23,7 +23,8 @@ trim_f(
 	char			**argv)
 {
 	struct fstrim_range	trim = {0};
-	struct xfs_fsop_geom	*fsgeom = &file->xfd.fsgeom;
+	struct xfs_fd		*xfd = &file->xfd;
+	struct xfs_fsop_geom	*fsgeom = &xfd->fsgeom;
 	xfs_agnumber_t		agno = 0;
 	off64_t			offset = 0;
 	ssize_t			length = 0;
@@ -66,11 +67,11 @@ trim_f(
 		length = cvtnum(fsgeom->blocksize, fsgeom->sectsize,
 				argv[optind + 1]);
 	} else if (agno) {
-		offset = (off64_t)agno * fsgeom->agblocks * fsgeom->blocksize;
-		length = fsgeom->agblocks * fsgeom->blocksize;
+		offset = xfrog_bbtob(xfrog_agb_to_daddr(xfd, agno, 0));
+		length = xfrog_fsb_to_b(xfd, fsgeom->agblocks);
 	} else {
 		offset = 0;
-		length = fsgeom->datablocks * fsgeom->blocksize;
+		length = xfrog_fsb_to_b(xfd, fsgeom->datablocks);
 	}
 
 	trim.start = offset;
