diff --git a/app/vmalert/alerting.go b/app/vmalert/alerting.go
index 51b6807cc..c5490bd42 100644
--- a/app/vmalert/alerting.go
+++ b/app/vmalert/alerting.go
@@ -42,6 +42,9 @@ type AlertingRule struct {
 	// resets on every successful Exec
 	// may be used as Health state
 	lastExecError error
+	// stores the number of samples returned during
+	// the last evaluation
+	lastExecSamples int
 
 	metrics *alertingRuleMetrics
 }
@@ -50,6 +53,7 @@ type alertingRuleMetrics struct {
 	errors  *gauge
 	pending *gauge
 	active  *gauge
+	samples *gauge
 }
 
 func newAlertingRule(qb datasource.QuerierBuilder, group *Group, cfg config.Rule) *AlertingRule {
@@ -76,8 +80,8 @@ func newAlertingRule(qb datasource.QuerierBuilder, group *Group, cfg config.Rule
 	labels := fmt.Sprintf(`alertname=%q, group=%q, id="%d"`, ar.Name, group.Name, ar.ID())
 	ar.metrics.pending = getOrCreateGauge(fmt.Sprintf(`vmalert_alerts_pending{%s}`, labels),
 		func() float64 {
-			ar.mu.Lock()
-			defer ar.mu.Unlock()
+			ar.mu.RLock()
+			defer ar.mu.RUnlock()
 			var num int
 			for _, a := range ar.alerts {
 				if a.State == notifier.StatePending {
@@ -88,8 +92,8 @@ func newAlertingRule(qb datasource.QuerierBuilder, group *Group, cfg config.Rule
 		})
 	ar.metrics.active = getOrCreateGauge(fmt.Sprintf(`vmalert_alerts_firing{%s}`, labels),
 		func() float64 {
-			ar.mu.Lock()
-			defer ar.mu.Unlock()
+			ar.mu.RLock()
+			defer ar.mu.RUnlock()
 			var num int
 			for _, a := range ar.alerts {
 				if a.State == notifier.StateFiring {
@@ -98,15 +102,21 @@ func newAlertingRule(qb datasource.QuerierBuilder, group *Group, cfg config.Rule
 			}
 			return float64(num)
 		})
-	ar.metrics.errors = getOrCreateGauge(fmt.Sprintf(`vmalert_alerts_error{%s}`, labels),
+	ar.metrics.errors = getOrCreateGauge(fmt.Sprintf(`vmalert_alerting_rules_error{%s}`, labels),
 		func() float64 {
-			ar.mu.Lock()
-			defer ar.mu.Unlock()
+			ar.mu.RLock()
+			defer ar.mu.RUnlock()
 			if ar.lastExecError == nil {
 				return 0
 			}
 			return 1
 		})
+	ar.metrics.samples = getOrCreateGauge(fmt.Sprintf(`vmalert_alerting_rules_last_evaluation_samples{%s}`, labels),
+		func() float64 {
+			ar.mu.RLock()
+			defer ar.mu.RUnlock()
+			return float64(ar.lastExecSamples)
+		})
 	return ar
 }
 
@@ -115,6 +125,7 @@ func (ar *AlertingRule) Close() {
 	metrics.UnregisterMetric(ar.metrics.active.name)
 	metrics.UnregisterMetric(ar.metrics.pending.name)
 	metrics.UnregisterMetric(ar.metrics.errors.name)
+	metrics.UnregisterMetric(ar.metrics.samples.name)
 }
 
 // String implements Stringer interface
@@ -194,6 +205,7 @@ func (ar *AlertingRule) Exec(ctx context.Context) ([]prompbmarshal.TimeSeries, e
 
 	ar.lastExecError = err
 	ar.lastExecTime = time.Now()
+	ar.lastExecSamples = len(qMetrics)
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute query %q: %w", ar.Expr, err)
 	}
@@ -384,6 +396,7 @@ func (ar *AlertingRule) RuleAPI() APIAlertingRule {
 		Expression:  ar.Expr,
 		For:         ar.For.String(),
 		LastError:   lastErr,
+		LastSamples: ar.lastExecSamples,
 		LastExec:    ar.lastExecTime,
 		Labels:      ar.Labels,
 		Annotations: ar.Annotations,
diff --git a/app/vmalert/recording.go b/app/vmalert/recording.go
index c5c70db50..0907be124 100644
--- a/app/vmalert/recording.go
+++ b/app/vmalert/recording.go
@@ -35,12 +35,16 @@ type RecordingRule struct {
 	// resets on every successful Exec
 	// may be used as Health state
 	lastExecError error
+	// stores the number of samples returned during
+	// the last evaluation
+	lastExecSamples int
 
 	metrics *recordingRuleMetrics
 }
 
 type recordingRuleMetrics struct {
-	errors *gauge
+	errors  *gauge
+	samples *gauge
 }
 
 // String implements Stringer interface
@@ -73,19 +77,26 @@ func newRecordingRule(qb datasource.QuerierBuilder, group *Group, cfg config.Rul
 	labels := fmt.Sprintf(`recording=%q, group=%q, id="%d"`, rr.Name, group.Name, rr.ID())
 	rr.metrics.errors = getOrCreateGauge(fmt.Sprintf(`vmalert_recording_rules_error{%s}`, labels),
 		func() float64 {
-			rr.mu.Lock()
-			defer rr.mu.Unlock()
+			rr.mu.RLock()
+			defer rr.mu.RUnlock()
 			if rr.lastExecError == nil {
 				return 0
 			}
 			return 1
 		})
+	rr.metrics.samples = getOrCreateGauge(fmt.Sprintf(`vmalert_recording_rules_last_evaluation_samples{%s}`, labels),
+		func() float64 {
+			rr.mu.RLock()
+			defer rr.mu.RUnlock()
+			return float64(rr.lastExecSamples)
+		})
 	return rr
 }
 
 // Close unregisters rule metrics
 func (rr *RecordingRule) Close() {
 	metrics.UnregisterMetric(rr.metrics.errors.name)
+	metrics.UnregisterMetric(rr.metrics.samples.name)
 }
 
 // ExecRange executes recording rule on the given time range similarly to Exec.
@@ -118,6 +129,7 @@ func (rr *RecordingRule) Exec(ctx context.Context) ([]prompbmarshal.TimeSeries,
 
 	rr.lastExecTime = time.Now()
 	rr.lastExecError = err
+	rr.lastExecSamples = len(qMetrics)
 	if err != nil {
 		return nil, fmt.Errorf("failed to execute query %q: %w", rr.Expr, err)
 	}
@@ -190,13 +202,14 @@ func (rr *RecordingRule) RuleAPI() APIRecordingRule {
 	}
 	return APIRecordingRule{
 		// encode as strings to avoid rounding
-		ID:         fmt.Sprintf("%d", rr.ID()),
-		GroupID:    fmt.Sprintf("%d", rr.GroupID),
-		Name:       rr.Name,
-		Type:       rr.Type.String(),
-		Expression: rr.Expr,
-		LastError:  lastErr,
-		LastExec:   rr.lastExecTime,
-		Labels:     rr.Labels,
+		ID:          fmt.Sprintf("%d", rr.ID()),
+		GroupID:     fmt.Sprintf("%d", rr.GroupID),
+		Name:        rr.Name,
+		Type:        rr.Type.String(),
+		Expression:  rr.Expr,
+		LastError:   lastErr,
+		LastSamples: rr.lastExecSamples,
+		LastExec:    rr.lastExecTime,
+		Labels:      rr.Labels,
 	}
 }
diff --git a/app/vmalert/web_types.go b/app/vmalert/web_types.go
index 8586fb64c..6b677ef8c 100644
--- a/app/vmalert/web_types.go
+++ b/app/vmalert/web_types.go
@@ -40,6 +40,7 @@ type APIAlertingRule struct {
 	Expression  string            `json:"expression"`
 	For         string            `json:"for"`
 	LastError   string            `json:"last_error"`
+	LastSamples int               `json:"last_samples"`
 	LastExec    time.Time         `json:"last_exec"`
 	Labels      map[string]string `json:"labels"`
 	Annotations map[string]string `json:"annotations"`
@@ -47,12 +48,13 @@ type APIAlertingRule struct {
 
 // APIRecordingRule represents RecordingRule for WEB view
 type APIRecordingRule struct {
-	ID         string            `json:"id"`
-	Name       string            `json:"name"`
-	Type       string            `json:"type"`
-	GroupID    string            `json:"group_id"`
-	Expression string            `json:"expression"`
-	LastError  string            `json:"last_error"`
-	LastExec   time.Time         `json:"last_exec"`
-	Labels     map[string]string `json:"labels"`
+	ID          string            `json:"id"`
+	Name        string            `json:"name"`
+	Type        string            `json:"type"`
+	GroupID     string            `json:"group_id"`
+	Expression  string            `json:"expression"`
+	LastError   string            `json:"last_error"`
+	LastSamples int               `json:"last_samples"`
+	LastExec    time.Time         `json:"last_exec"`
+	Labels      map[string]string `json:"labels"`
 }