diff --git a/CHANGES b/CHANGES
index d50ad9abb1..4792141124 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+6026.	[cleanup]	Deduplicate time unit conversion factors.
+			[GL !7033]
+
 6025.	[bug]		Copy TLS identifier when setting up primaries for
 			catalog member zones. [GL #3638]
 
diff --git a/bin/tools/mdig.c b/bin/tools/mdig.c
index 034331e953..b0bb6d122e 100644
--- a/bin/tools/mdig.c
+++ b/bin/tools/mdig.c
@@ -36,6 +36,7 @@
 #include <isc/sockaddr.h>
 #include <isc/string.h>
 #include <isc/task.h>
+#include <isc/time.h>
 #include <isc/util.h>
 
 #include <dns/byaddr.h>
@@ -84,10 +85,6 @@
 #define UDPTIMEOUT 5
 #define MAXTRIES   0xffffffff
 
-#define NS_PER_US  1000	   /*%< Nanoseconds per microsecond. */
-#define US_PER_SEC 1000000 /*%< Microseconds per second. */
-#define US_PER_MS  1000	   /*%< Microseconds per millisecond. */
-
 static isc_mem_t *mctx = NULL;
 static dns_requestmgr_t *requestmgr = NULL;
 static const char *batchname = NULL;
diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index f03dc612db..7901142d3e 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -28,6 +28,7 @@
 #include <isc/stats.h>
 #include <isc/string.h>
 #include <isc/task.h>
+#include <isc/time.h>
 #include <isc/timer.h>
 #include <isc/util.h>
 
@@ -170,14 +171,11 @@
 #define fctx_addref(f) fctx_attach((f), &(fetchctx_t *){ NULL })
 #define fctx_unref(f)  fctx_detach(&(fetchctx_t *){ (f) })
 
-#define US_PER_SEC  1000000U
-#define US_PER_MSEC 1000U
-#define NS_PER_US   1000U
 /*
  * The maximum time we will wait for a single query.
  */
 #define MAX_SINGLE_QUERY_TIMEOUT    9000U
-#define MAX_SINGLE_QUERY_TIMEOUT_US (MAX_SINGLE_QUERY_TIMEOUT * US_PER_MSEC)
+#define MAX_SINGLE_QUERY_TIMEOUT_US (MAX_SINGLE_QUERY_TIMEOUT * US_PER_MS)
 
 /*
  * We need to allow a individual query time to complete / timeout.
@@ -1348,7 +1346,7 @@ fctx_cancelquery(resquery_t **queryp, isc_time_t *finish, bool no_response,
 							       &query->start);
 			factor = DNS_ADB_RTTADJDEFAULT;
 
-			rttms = rtt / US_PER_MSEC;
+			rttms = rtt / US_PER_MS;
 			if (rttms < DNS_RESOLVER_QRYRTTCLASS0) {
 				inc_stats(fctx->res,
 					  dns_resstatscounter_queryrtt0);
@@ -1960,13 +1958,13 @@ fctx_setretryinterval(fetchctx_t *fctx, unsigned int rtt) {
 	 */
 	isc_time_now(&now);
 	limit = isc_time_microdiff(&fctx->expires, &now);
-	if (limit < US_PER_MSEC) {
+	if (limit < US_PER_MS) {
 		FCTXTRACE("fetch already expired");
 		isc_interval_set(&fctx->interval, 0, 0);
 		return;
 	}
 
-	us = fctx->res->retryinterval * US_PER_MSEC;
+	us = fctx->res->retryinterval * US_PER_MS;
 
 	/*
 	 * Exponential backoff after the first few tries.
@@ -2005,7 +2003,7 @@ fctx_setretryinterval(fetchctx_t *fctx, unsigned int rtt) {
 	if ((fctx->options & DNS_FETCHOPT_TRYSTALE_ONTIMEOUT) != 0) {
 		uint64_t stale = isc_time_microdiff(&fctx->expires_try_stale,
 						    &now);
-		if (stale >= US_PER_MSEC && us > stale) {
+		if (stale >= US_PER_MS && us > stale) {
 			FCTXTRACE("setting stale timeout");
 			us = stale;
 		}
@@ -2046,7 +2044,7 @@ resquery_timeout(resquery_t *query) {
 	 */
 	isc_time_now(&now);
 	timeleft = isc_time_microdiff(&fctx->expires_try_stale, &now);
-	if (timeleft >= US_PER_MSEC) {
+	if (timeleft >= US_PER_MS) {
 		return (ISC_R_SUCCESS);
 	}
 
@@ -2075,8 +2073,8 @@ resquery_timeout(resquery_t *query) {
 	 * resume waiting.
 	 */
 	timeleft = isc_time_microdiff(&fctx->next_timeout, &now);
-	if (timeleft >= US_PER_MSEC) {
-		dns_dispatch_resume(query->dispentry, (timeleft / US_PER_MSEC));
+	if (timeleft >= US_PER_MS) {
+		dns_dispatch_resume(query->dispentry, (timeleft / US_PER_MS));
 		return (ISC_R_COMPLETE);
 	}
 
@@ -8181,7 +8179,7 @@ rctx_timedout(respctx_t *rctx) {
 
 		isc_time_now(&now);
 		/* netmgr timeouts are accurate to the millisecond */
-		if (isc_time_microdiff(&fctx->expires, &now) < US_PER_MSEC) {
+		if (isc_time_microdiff(&fctx->expires, &now) < US_PER_MS) {
 			FCTXTRACE("stopped trying to make fetch happen");
 		} else {
 			FCTXTRACE("query timed out; no response");
diff --git a/lib/isc/include/isc/time.h b/lib/isc/include/isc/time.h
index 8416927f02..9c9da37378 100644
--- a/lib/isc/include/isc/time.h
+++ b/lib/isc/include/isc/time.h
@@ -21,6 +21,15 @@
 #include <isc/lang.h>
 #include <isc/types.h>
 
+enum {
+	MS_PER_SEC = 1000,		 /*%< Milliseonds per second. */
+	US_PER_MS = 1000,		 /*%< Microseconds per millisecond. */
+	US_PER_SEC = 1000 * 1000,	 /*%< Microseconds per second. */
+	NS_PER_US = 1000,		 /*%< Nanoseconds per millisecond. */
+	NS_PER_MS = 1000 * 1000,	 /*%< Nanoseconds per microsecond. */
+	NS_PER_SEC = 1000 * 1000 * 1000, /*%< Nanoseconds per second. */
+};
+
 /***
  *** Intervals
  ***/
diff --git a/lib/isc/stdtime.c b/lib/isc/stdtime.c
index 574d149b67..b7cec81842 100644
--- a/lib/isc/stdtime.c
+++ b/lib/isc/stdtime.c
@@ -21,10 +21,9 @@
 #include <time.h>
 
 #include <isc/stdtime.h>
+#include <isc/time.h>
 #include <isc/util.h>
 
-#define NS_PER_S 1000000000 /*%< Nanoseconds per second. */
-
 #if defined(CLOCK_REALTIME_COARSE)
 #define CLOCKSOURCE CLOCK_REALTIME_COARSE
 #elif defined(CLOCK_REALTIME_FAST)
@@ -43,7 +42,7 @@ isc_stdtime_get(isc_stdtime_t *t) {
 		FATAL_SYSERROR(errno, "clock_gettime()");
 	}
 
-	REQUIRE(ts.tv_sec > 0 && ts.tv_nsec >= 0 && ts.tv_nsec < NS_PER_S);
+	REQUIRE(ts.tv_sec > 0 && ts.tv_nsec >= 0 && ts.tv_nsec < NS_PER_SEC);
 
 	*t = (isc_stdtime_t)ts.tv_sec;
 }
diff --git a/lib/isc/time.c b/lib/isc/time.c
index 05c67ffc0a..b03f377a3e 100644
--- a/lib/isc/time.c
+++ b/lib/isc/time.c
@@ -29,11 +29,6 @@
 #include <isc/tm.h>
 #include <isc/util.h>
 
-#define NS_PER_S  1000000000 /*%< Nanoseconds per second. */
-#define NS_PER_US 1000	     /*%< Nanoseconds per microsecond. */
-#define NS_PER_MS 1000000    /*%< Nanoseconds per millisecond. */
-#define MS_PER_S  1000	     /*%< Milliseonds per second. */
-
 #if defined(CLOCK_REALTIME)
 #define CLOCKSOURCE_HIRES CLOCK_REALTIME
 #endif /* #if defined(CLOCK_REALTIME) */
@@ -63,7 +58,7 @@ void
 isc_interval_set(isc_interval_t *i, unsigned int seconds,
 		 unsigned int nanoseconds) {
 	REQUIRE(i != NULL);
-	REQUIRE(nanoseconds < NS_PER_S);
+	REQUIRE(nanoseconds < NS_PER_SEC);
 
 	i->seconds = seconds;
 	i->nanoseconds = nanoseconds;
@@ -72,7 +67,7 @@ isc_interval_set(isc_interval_t *i, unsigned int seconds,
 bool
 isc_interval_iszero(const isc_interval_t *i) {
 	REQUIRE(i != NULL);
-	INSIST(i->nanoseconds < NS_PER_S);
+	INSIST(i->nanoseconds < NS_PER_SEC);
 
 	if (i->seconds == 0 && i->nanoseconds == 0) {
 		return (true);
@@ -84,9 +79,9 @@ isc_interval_iszero(const isc_interval_t *i) {
 unsigned int
 isc_interval_ms(const isc_interval_t *i) {
 	REQUIRE(i != NULL);
-	INSIST(i->nanoseconds < NS_PER_S);
+	INSIST(i->nanoseconds < NS_PER_SEC);
 
-	return ((i->seconds * MS_PER_S) + (i->nanoseconds / NS_PER_MS));
+	return ((i->seconds * MS_PER_SEC) + (i->nanoseconds / NS_PER_MS));
 }
 
 /***
@@ -101,7 +96,7 @@ const isc_time_t *const isc_time_epoch = &epoch;
 void
 isc_time_set(isc_time_t *t, unsigned int seconds, unsigned int nanoseconds) {
 	REQUIRE(t != NULL);
-	REQUIRE(nanoseconds < NS_PER_S);
+	REQUIRE(nanoseconds < NS_PER_SEC);
 
 	t->seconds = seconds;
 	t->nanoseconds = nanoseconds;
@@ -118,7 +113,7 @@ isc_time_settoepoch(isc_time_t *t) {
 bool
 isc_time_isepoch(const isc_time_t *t) {
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 
 	if (t->seconds == 0 && t->nanoseconds == 0) {
 		return (true);
@@ -138,7 +133,7 @@ time_now(isc_time_t *t, clockid_t clock) {
 		return (ISC_R_UNEXPECTED);
 	}
 
-	if (ts.tv_sec < 0 || ts.tv_nsec < 0 || ts.tv_nsec >= NS_PER_S) {
+	if (ts.tv_sec < 0 || ts.tv_nsec < 0 || ts.tv_nsec >= NS_PER_SEC) {
 		return (ISC_R_UNEXPECTED);
 	}
 
@@ -173,14 +168,14 @@ isc_time_nowplusinterval(isc_time_t *t, const isc_interval_t *i) {
 
 	REQUIRE(t != NULL);
 	REQUIRE(i != NULL);
-	INSIST(i->nanoseconds < NS_PER_S);
+	INSIST(i->nanoseconds < NS_PER_SEC);
 
 	if (clock_gettime(CLOCKSOURCE, &ts) == -1) {
 		UNEXPECTED_SYSERROR(errno, "clock_gettime()");
 		return (ISC_R_UNEXPECTED);
 	}
 
-	if (ts.tv_sec < 0 || ts.tv_nsec < 0 || ts.tv_nsec >= NS_PER_S) {
+	if (ts.tv_sec < 0 || ts.tv_nsec < 0 || ts.tv_nsec >= NS_PER_SEC) {
 		return (ISC_R_UNEXPECTED);
 	}
 
@@ -198,9 +193,9 @@ isc_time_nowplusinterval(isc_time_t *t, const isc_interval_t *i) {
 
 	t->seconds = ts.tv_sec + i->seconds;
 	t->nanoseconds = ts.tv_nsec + i->nanoseconds;
-	if (t->nanoseconds >= NS_PER_S) {
+	if (t->nanoseconds >= NS_PER_SEC) {
 		t->seconds++;
-		t->nanoseconds -= NS_PER_S;
+		t->nanoseconds -= NS_PER_SEC;
 	}
 
 	return (ISC_R_SUCCESS);
@@ -209,7 +204,7 @@ isc_time_nowplusinterval(isc_time_t *t, const isc_interval_t *i) {
 int
 isc_time_compare(const isc_time_t *t1, const isc_time_t *t2) {
 	REQUIRE(t1 != NULL && t2 != NULL);
-	INSIST(t1->nanoseconds < NS_PER_S && t2->nanoseconds < NS_PER_S);
+	INSIST(t1->nanoseconds < NS_PER_SEC && t2->nanoseconds < NS_PER_SEC);
 
 	if (t1->seconds < t2->seconds) {
 		return (-1);
@@ -229,7 +224,7 @@ isc_time_compare(const isc_time_t *t1, const isc_time_t *t2) {
 isc_result_t
 isc_time_add(const isc_time_t *t, const isc_interval_t *i, isc_time_t *result) {
 	REQUIRE(t != NULL && i != NULL && result != NULL);
-	REQUIRE(t->nanoseconds < NS_PER_S && i->nanoseconds < NS_PER_S);
+	REQUIRE(t->nanoseconds < NS_PER_SEC && i->nanoseconds < NS_PER_SEC);
 
 	/* Seconds */
 #if HAVE_BUILTIN_OVERFLOW
@@ -245,11 +240,11 @@ isc_time_add(const isc_time_t *t, const isc_interval_t *i, isc_time_t *result) {
 
 	/* Nanoseconds */
 	result->nanoseconds = t->nanoseconds + i->nanoseconds;
-	if (result->nanoseconds >= NS_PER_S) {
+	if (result->nanoseconds >= NS_PER_SEC) {
 		if (result->seconds == UINT_MAX) {
 			return (ISC_R_RANGE);
 		}
-		result->nanoseconds -= NS_PER_S;
+		result->nanoseconds -= NS_PER_SEC;
 		result->seconds++;
 	}
 
@@ -260,7 +255,7 @@ isc_result_t
 isc_time_subtract(const isc_time_t *t, const isc_interval_t *i,
 		  isc_time_t *result) {
 	REQUIRE(t != NULL && i != NULL && result != NULL);
-	REQUIRE(t->nanoseconds < NS_PER_S && i->nanoseconds < NS_PER_S);
+	REQUIRE(t->nanoseconds < NS_PER_SEC && i->nanoseconds < NS_PER_SEC);
 
 	/* Seconds */
 #if HAVE_BUILTIN_OVERFLOW
@@ -282,7 +277,7 @@ isc_time_subtract(const isc_time_t *t, const isc_interval_t *i,
 			return (ISC_R_RANGE);
 		}
 		result->seconds--;
-		result->nanoseconds = NS_PER_S + t->nanoseconds -
+		result->nanoseconds = NS_PER_SEC + t->nanoseconds -
 				      i->nanoseconds;
 	}
 
@@ -294,10 +289,10 @@ isc_time_microdiff(const isc_time_t *t1, const isc_time_t *t2) {
 	uint64_t i1, i2, i3;
 
 	REQUIRE(t1 != NULL && t2 != NULL);
-	INSIST(t1->nanoseconds < NS_PER_S && t2->nanoseconds < NS_PER_S);
+	INSIST(t1->nanoseconds < NS_PER_SEC && t2->nanoseconds < NS_PER_SEC);
 
-	i1 = (uint64_t)t1->seconds * NS_PER_S + t1->nanoseconds;
-	i2 = (uint64_t)t2->seconds * NS_PER_S + t2->nanoseconds;
+	i1 = (uint64_t)t1->seconds * NS_PER_SEC + t1->nanoseconds;
+	i2 = (uint64_t)t2->seconds * NS_PER_SEC + t2->nanoseconds;
 
 	if (i1 <= i2) {
 		return (0);
@@ -316,7 +311,7 @@ isc_time_microdiff(const isc_time_t *t1, const isc_time_t *t2) {
 uint32_t
 isc_time_seconds(const isc_time_t *t) {
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 
 	return ((uint32_t)t->seconds);
 }
@@ -326,7 +321,7 @@ isc_time_secondsastimet(const isc_time_t *t, time_t *secondsp) {
 	time_t seconds;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 
 	/*
 	 * Ensure that the number of seconds represented by t->seconds
@@ -363,7 +358,7 @@ uint32_t
 isc_time_nanoseconds(const isc_time_t *t) {
 	REQUIRE(t != NULL);
 
-	ENSURE(t->nanoseconds < NS_PER_S);
+	ENSURE(t->nanoseconds < NS_PER_SEC);
 
 	return ((uint32_t)t->nanoseconds);
 }
@@ -375,7 +370,7 @@ isc_time_formattimestamp(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -397,7 +392,7 @@ isc_time_formathttptimestamp(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -439,7 +434,7 @@ isc_time_formatISO8601L(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -455,7 +450,7 @@ isc_time_formatISO8601Lms(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -475,7 +470,7 @@ isc_time_formatISO8601Lus(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -495,7 +490,7 @@ isc_time_formatISO8601(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -511,7 +506,7 @@ isc_time_formatISO8601ms(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -532,7 +527,7 @@ isc_time_formatISO8601us(const isc_time_t *t, char *buf, unsigned int len) {
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
@@ -554,7 +549,7 @@ isc_time_formatshorttimestamp(const isc_time_t *t, char *buf,
 	struct tm tm;
 
 	REQUIRE(t != NULL);
-	INSIST(t->nanoseconds < NS_PER_S);
+	INSIST(t->nanoseconds < NS_PER_SEC);
 	REQUIRE(buf != NULL);
 	REQUIRE(len > 0);
 
diff --git a/tests/isc/time_test.c b/tests/isc/time_test.c
index 4b355a7003..70858e90d6 100644
--- a/tests/isc/time_test.c
+++ b/tests/isc/time_test.c
@@ -30,8 +30,7 @@
 
 #include <tests/isc.h>
 
-#define NS_PER_S 1000000000 /*%< Nanoseconds per second. */
-#define MAX_NS	 (NS_PER_S - 1)
+#define MAX_NS (NS_PER_SEC - 1)
 
 struct time_vectors {
 	isc_time_t a;
@@ -43,13 +42,16 @@ struct time_vectors {
 const struct time_vectors vectors_add[8] = {
 	{ { 0, 0 }, { 0, 0 }, { 0, 0 }, ISC_R_SUCCESS },
 	{ { 0, MAX_NS }, { 0, MAX_NS }, { 1, MAX_NS - 1 }, ISC_R_SUCCESS },
-	{ { 0, NS_PER_S / 2 }, { 0, NS_PER_S / 2 }, { 1, 0 }, ISC_R_SUCCESS },
+	{ { 0, NS_PER_SEC / 2 },
+	  { 0, NS_PER_SEC / 2 },
+	  { 1, 0 },
+	  ISC_R_SUCCESS },
 	{ { UINT_MAX, MAX_NS }, { 0, 0 }, { UINT_MAX, MAX_NS }, ISC_R_SUCCESS },
 	{ { UINT_MAX, 0 }, { 0, MAX_NS }, { UINT_MAX, MAX_NS }, ISC_R_SUCCESS },
 	{ { UINT_MAX, 0 }, { 1, 0 }, { 0, 0 }, ISC_R_RANGE },
 	{ { UINT_MAX, MAX_NS }, { 0, 1 }, { 0, 0 }, ISC_R_RANGE },
-	{ { UINT_MAX / 2 + 1, NS_PER_S / 2 },
-	  { UINT_MAX / 2, NS_PER_S / 2 },
+	{ { UINT_MAX / 2 + 1, NS_PER_SEC / 2 },
+	  { UINT_MAX / 2, NS_PER_SEC / 2 },
 	  { 0, 0 },
 	  ISC_R_RANGE },
 };
@@ -57,9 +59,9 @@ const struct time_vectors vectors_add[8] = {
 const struct time_vectors vectors_sub[7] = {
 	{ { 0, 0 }, { 0, 0 }, { 0, 0 }, ISC_R_SUCCESS },
 	{ { 1, 0 }, { 0, MAX_NS }, { 0, 1 }, ISC_R_SUCCESS },
-	{ { 1, NS_PER_S / 2 },
+	{ { 1, NS_PER_SEC / 2 },
 	  { 0, MAX_NS },
-	  { 0, NS_PER_S / 2 + 1 },
+	  { 0, NS_PER_SEC / 2 + 1 },
 	  ISC_R_SUCCESS },
 	{ { UINT_MAX, MAX_NS }, { UINT_MAX, 0 }, { 0, MAX_NS }, ISC_R_SUCCESS },
 	{ { 0, 0 }, { 1, 0 }, { 0, 0 }, ISC_R_RANGE },