diff --git a/modules/archive.sh b/modules/archive.sh
index b6be4aa..3df2d7f 100755
--- a/modules/archive.sh
+++ b/modules/archive.sh
@@ -44,18 +44,16 @@ calc_smart_volumes() {
 	total_size=$(du -s -BM "${input_file}" | grep -oP '^\d+') || return 0
 
 	# If total file size is smaller than volume size, don't pack it into volumes
-	[[ $total_size -lt $size ]] && return 1
+	(( total_size < size )) && return 1
 
-	num_volumes=$(echo "($total_size + $size - 1) / $size" | bc)
-	size=$(echo "($total_size + $num_volumes - 1) / $num_volumes" | bc)
+	num_volumes=$(( (total_size + size - 1) / size ))
+	size=$(( (total_size + num_volumes - 1) / num_volumes ))
 
 	echo "Calculated smart volume size '$size'" >&2
 }
 
 set_volumes() {
-	if [[ -n "$size" ]]; then
-		calc_smart_volumes && volumes="-v${size}m"
-	fi
+	[[ -n "$size" ]] && calc_smart_volumes && volumes="-v${size}m"
 
 	echo "Volumes set to '$volumes'" >&2
 }