diff --git a/include/f2fs_fs.h b/include/f2fs_fs.h
index 38a774c..359deec 100644
--- a/include/f2fs_fs.h
+++ b/include/f2fs_fs.h
@@ -225,7 +225,7 @@ enum f2fs_config_func {
 struct f2fs_configuration {
 	u_int32_t sector_size;
 	u_int32_t reserved_segments;
-	u_int32_t overprovision;
+	double overprovision;
 	u_int32_t cur_seg[6];
 	u_int32_t segs_per_sec;
 	u_int32_t secs_per_zone;
diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
index 2d4ab09..176bdea 100644
--- a/mkfs/f2fs_format.c
+++ b/mkfs/f2fs_format.c
@@ -155,19 +155,19 @@ static void configure_extension_list(void)
 	free(config.extension_list);
 }
 
-static u_int32_t get_best_overprovision(void)
+static double get_best_overprovision(void)
 {
-	u_int32_t reserved, ovp, candidate, end, diff, space;
-	u_int32_t max_ovp = 0, max_space = 0;
+	double reserved, ovp, candidate, end, diff, space;
+	double max_ovp = 0, max_space = 0;
 
 	if (get_sb(segment_count_main) < 256) {
 		candidate = 10;
 		end = 95;
 		diff = 5;
 	} else {
-		candidate = 1;
+		candidate = 0.01;
 		end = 10;
-		diff = 1;
+		diff = 0.01;
 	}
 
 	for (; candidate <= end; candidate += diff) {
@@ -533,7 +533,7 @@ static int f2fs_write_check_point_pack(void)
 	set_cp(overprov_segment_count, get_cp(overprov_segment_count) +
 			get_cp(rsvd_segment_count));
 
-	MSG(0, "Info: Overprovision ratio = %u%%\n", config.overprovision);
+	MSG(0, "Info: Overprovision ratio = %.3lf%%\n", config.overprovision);
 	MSG(0, "Info: Overprovision segments = %u (GC reserved = %u)\n",
 					get_cp(overprov_segment_count),
 					config.reserved_segments);
diff --git a/mkfs/f2fs_format_main.c b/mkfs/f2fs_format_main.c
index fc612d8..2ea809c 100644
--- a/mkfs/f2fs_format_main.c
+++ b/mkfs/f2fs_format_main.c
@@ -99,7 +99,7 @@ static void f2fs_parse_options(int argc, char *argv[])
 			config.vol_label = optarg;
 			break;
 		case 'o':
-			config.overprovision = atoi(optarg);
+			config.overprovision = atof(optarg);
 			break;
 		case 'O':
 			parse_feature(strdup(optarg));