How to get length / size of NVS value on ESP32

You can find the size of a value stored in ESP32 NVS by running nvs_get_blob() with length set to a pointer to a variable with content 0, and out_value set to nullptrnvs_get_str() works as well, the only difference is the type of the out_value argument, which does not matter at all.

It’s easier to understand if you look at this example function:

size_t NVSGetSize(nvs_handle_t nvs, const char* key) {
    esp_err_t err;
    size_t valueSize = 0;
    if((err = nvs_get_str(nvs, key, nullptr, &valueSize)) != ESP_OK) {
        if(err == ESP_ERR_NVS_NOT_FOUND) {
            // Not found, no error
            return 0;
        } else {
             // Actual error, log & return 0
            printf("Failed to get size of NVS key %s: %s\r\n", key, esp_err_to_name(err));
            return 0;
    return valueSize;

Usage example

This assumes that you have setup myNvs as we have shown in our previous post How to initialize NVS on ESP32

size_t myKeySize = NVSGetSize(myNvs, "MyKey");