diff --git a/sys/net80211/ieee80211_phy.h b/sys/net80211/ieee80211_phy.h
--- a/sys/net80211/ieee80211_phy.h
+++ b/sys/net80211/ieee80211_phy.h
@@ -221,5 +221,12 @@
 			uint16_t rate, int streams, int isht40,
 			int isShortGI);
 
+enum ieee80211_sta_rx_bw;
+
+uint16_t	ieee80211_phy_vht_get_mcs_mask(enum ieee80211_sta_rx_bw,
+		    uint8_t);
+bool		ieee80211_phy_vht_validate_mcs(enum ieee80211_sta_rx_bw,
+		    uint8_t, uint8_t);
+
 #endif	/* _KERNEL */
 #endif	/* !_NET80211_IEEE80211_PHY_H_ */
diff --git a/sys/net80211/ieee80211_phy.c b/sys/net80211/ieee80211_phy.c
--- a/sys/net80211/ieee80211_phy.c
+++ b/sys/net80211/ieee80211_phy.c
@@ -621,3 +621,89 @@
 #undef	HT_L_LTF
 #undef	HT_L_STF
 #undef	OFDM_PLCP_BITS
+
+
+/*
+ * A bitmask of allowable rates for each spatial stream
+ * and bandwidth.
+ *
+ * This is based on 802.11-2020 21.5 (Parameters for VHT-MCSs.)
+ *
+ * Not all MCS rate / channel widths are valid, as there needs
+ * to be an integer number of symbols and the number of tones
+ * available for each channel bandwidth doesn't result in
+ * an integer value.
+ */
+static uint16_t ieee80211_vht_mcs_allowed_list_20[] = {
+	0x01ff, 0x01ff, 0x03ff, 0x01ff, 0x01ff, 0x03ff, 0x01ff, 0x01ff,
+};
+
+static uint16_t ieee80211_vht_mcs_allowed_list_40[] = {
+	0x03ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff,
+};
+
+static uint16_t ieee80211_vht_mcs_allowed_list_80[] = {
+	0x03ff, 0x03ff, 0x03bf, 0x03ff, 0x03ff, 0x01ff, 0x03bf, 0x03ff,
+};
+
+static uint16_t ieee80211_vht_mcs_allowed_list_160[] = {
+	0x03ff, 0x03ff, 0x01ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff, 0x03ff,
+};
+
+/**
+ * @brief Fetch the allowable MCS mask for the given channel bandwidth and NSS
+ *
+ * Return a bitmask of valid MCS rates from 0..9 given a channel bandwith
+ * and number of spatial streams.
+ *
+ * See 802.11-2020 21.5 (Parameters for VHT-MCSs) for more details.
+ *
+ * @param bw	channel bandwidth, via enum ieee80211_sta_rx_bw
+ * @param nss	number of spatial streams, 1..8
+ * @returns	bitmask of valid MCS rates from 0..9
+ */
+uint16_t
+ieee80211_phy_vht_get_mcs_mask(enum ieee80211_sta_rx_bw bw, uint8_t nss)
+{
+	if (nss == 0 || nss > 8)
+		return (0);
+
+	switch (bw) {
+	case IEEE80211_STA_RX_BW_20:
+		return (ieee80211_vht_mcs_allowed_list_20[nss - 1]);
+	case IEEE80211_STA_RX_BW_40:
+		return (ieee80211_vht_mcs_allowed_list_40[nss - 1]);
+	case IEEE80211_STA_RX_BW_80:
+		return (ieee80211_vht_mcs_allowed_list_80[nss - 1]);
+	case IEEE80211_STA_RX_BW_160:
+		return (ieee80211_vht_mcs_allowed_list_160[nss - 1]);
+	case IEEE80211_STA_RX_BW_320:
+		/* invalid for VHT */
+		return (0);
+	}
+}
+
+/**
+ * @brief Check if the given NSS/MCS combination is valid for the given channel
+ * bandwidth
+ *
+ * See 802.11-2020 21.5 (Parameters for VHT-MCSs) for more details.
+ *
+ * @param bw	channel bandwidth, via enum ieee80211_sta_rx_bw
+ * @param nss	number of spatial streams, 1..8
+ * @param mcs	MCS rate, 0..9
+ * @retval true		if the NSS / MCS / bandwidth combination is valid
+ * @retval false	if the NSS / MCS / bandwidth combination is not valid
+ */
+bool
+ieee80211_phy_vht_validate_mcs(enum ieee80211_sta_rx_bw bw, uint8_t nss,
+    uint8_t mcs)
+{
+	uint16_t mask;
+
+	mask = ieee80211_phy_vht_get_mcs_mask(bw, nss);
+	if (mask == 0)
+		return (false);
+
+	return ((mask & (1 << mcs)) != 0);
+}