diff --git a/usr.sbin/newsyslog/Makefile b/usr.sbin/newsyslog/Makefile
index 0afbe3b814a7..26ff30d4a0b3 100644
--- a/usr.sbin/newsyslog/Makefile
+++ b/usr.sbin/newsyslog/Makefile
@@ -6,7 +6,7 @@ CONFS=	newsyslog.conf
 PROG=	newsyslog
 MAN=	newsyslog.8 newsyslog.conf.5
 SRCS=	newsyslog.c ptimes.c
-LIBADD=	sbuf
+LIBADD=	sbuf util
 
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
diff --git a/usr.sbin/newsyslog/newsyslog.c b/usr.sbin/newsyslog/newsyslog.c
index e9b84bae342d..d07f302fd24f 100644
--- a/usr.sbin/newsyslog/newsyslog.c
+++ b/usr.sbin/newsyslog/newsyslog.c
@@ -77,6 +77,7 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <libgen.h>
+#include <libutil.h>
 #include <stdlib.h>
 #include <string.h>
 #include <syslog.h>
@@ -1335,9 +1336,21 @@ parse_file(FILE *cf, struct cflist *work_p, struct cflist *glob_p,
 			badline("malformed line (missing fields):\n%s",
 			    errline);
 		*parse = '\0';
-		if (isdigitch(*q))
-			working->trsize = atoi(q);
-		else if (strcmp(q, "*") == 0)
+		if (isdigitch(*q)) {
+			char last_digit = q[strlen(q) - 1];
+			if (isdigitch(last_digit))
+				working->trsize = atoi(q);
+			else {
+				uint64_t trsize = 0;
+				if (expand_number(q, &trsize) == 0)
+					working->trsize = trsize / 1024;
+				else {
+					working->trsize = -1;
+					warnx("Invalid value of '%s' for 'size' in line:\n%s",
+						q, errline);
+				}
+			}
+		} else if (strcmp(q, "*") == 0)
 			working->trsize = -1;
 		else {
 			warnx("Invalid value of '%s' for 'size' in line:\n%s",
diff --git a/usr.sbin/newsyslog/newsyslog.conf.5 b/usr.sbin/newsyslog/newsyslog.conf.5
index a8ab132edaa8..a9deb079e294 100644
--- a/usr.sbin/newsyslog/newsyslog.conf.5
+++ b/usr.sbin/newsyslog/newsyslog.conf.5
@@ -18,7 +18,7 @@
 .\" the suitability of this software for any purpose.  It is
 .\" provided "as is" without express or implied warranty.
 .\"
-.Dd December 25, 2023
+.Dd November 11, 2024
 .Dt NEWSYSLOG.CONF 5
 .Os
 .Sh NAME
@@ -116,8 +116,10 @@ Specify the maximum number of archive files which may exist.
 This does not consider the current log file.
 .It Ar size
 When the size of the log file reaches
-.Ar size
-in kilobytes, the log file will be trimmed as described above.
+.Ar size ,
+in kilobytes by default, or with suffix suffixes like k, M, G, ... as supported by
+.Xr expand_number 3 ,
+the log file will be trimmed as described above.
 If this field contains an asterisk
 .Pq Ql * ,
 the log file will not be trimmed based on size.
@@ -438,6 +440,7 @@ entry:
 .Xr gzip 1 ,
 .Xr xz 1 ,
 .Xr zstd 1 ,
+.Xr expand_number 3 ,
 .Xr syslog 3 ,
 .Xr chown 8 ,
 .Xr newsyslog 8 ,