diff --git a/esphome/components/esp8266/const.py b/esphome/components/esp8266/const.py
index fb50b6a5ca2..a702b397049 100644
--- a/esphome/components/esp8266/const.py
+++ b/esphome/components/esp8266/const.py
@@ -24,6 +24,12 @@ KEY_LDSCRIPT = "ldscript"
 # Crash-decode tools, resolved once per run by __init__
 KEY_DECODE_TOOLS = "decode_tools"
 
+# Space for saved settings, in 4-byte words, from preferences.cpp: RTC memory has two regions
+# (RTC_NORMAL_REGION_WORDS, RTC_EBOOT_REGION_WORDS) that one saved value cannot span; with
+# restore_from_flash everything goes to flash (ESP8266_FLASH_STORAGE_SIZE)
+PREFERENCES_RTC_REGION_WORDS = (78, 32)
+PREFERENCES_FLASH_WORDS = 128
+
 # esp8266 namespace is already defined by arduino, manually prefix esphome
 esp8266_ns = cg.global_ns.namespace("esphome").namespace("esp8266")
 
diff --git a/esphome/components/esp8266/preferences.cpp b/esphome/components/esp8266/preferences.cpp
index b731187f9c3..dbfb233a1d4 100644
--- a/esphome/components/esp8266/preferences.cpp
+++ b/esphome/components/esp8266/preferences.cpp
@@ -24,6 +24,7 @@ static constexpr uint32_t ESP_RTC_USER_MEM_SIZE_BYTES = ESP_RTC_USER_MEM_SIZE_WO
 // - Eboot region:  RTC words 0-31   (reserved, mapped from preference offset 78-109)
 // - Normal region: RTC words 32-109 (mapped from preference offset 0-77)
 // - Crash handler: RTC words 110-127 (reserved for crash_handler.cpp backtrace data)
+// const.py mirrors the region and flash sizes for config-time space checks
 static constexpr uint32_t RTC_EBOOT_REGION_WORDS = 32;   // Words 0-31 reserved for eboot
 static constexpr uint32_t RTC_NORMAL_REGION_WORDS = 78;  // Words 32-109 for normal prefs
 static constexpr uint32_t PREF_TOTAL_WORDS = RTC_EBOOT_REGION_WORDS + RTC_NORMAL_REGION_WORDS;  // 110