Small example how to add stats counting to a SFML `sf::RenderWindow`. Release builds could just use `sf::RenderWindow` directly instead. Note this isn't necessarily 100% perfect or correct; written from memory.

statswindow.cpp

#include <SFML/Graphics.hpp>
#include <sstream>

class RenderWindowStats : public sf::RenderWindow {
public:
    RenderWindowStats() : RenderWindow({640, 480}, "Test") {
    }

    void draw(sf::Drawable &dr, sf::RenderStates states = sf::RenderStates()) {
        ++mDrawCallsTemp;
        sf::RenderWindow::draw(dr, states);

        if (mTimer.getElapsedTime() > sf::seconds(1)) {
            mDrawCalls = mDrawCallsTemp;
            mDrawCallsTemp = 0;
            mFrames = mFramesTemp;
            mFramesTemp = 0;

            mTimer.restart();
        }
    }

    void display() {
        ++mFramesTemp;
        sf::RenderWindow::display();
    }

    std::size_t getDrawCallsPerSecond() const { return mDrawCalls; }
    std::size_t getFramesPerSecond() const { return mFrames; }
private:
    std::size_t mDrawCallsTemp = 0;
    std::size_t mDrawCalls = 0;
    std::size_t mFramesTemp = 0;
    std::size_t mFrames = 0;
    sf::Clock mTimer;
};

int main(int argc, char **argv) {
    RenderWindowStats window;
    window.setVerticalSyncEnabled(true);

    sf::Font font; font.loadFromFile("C:/Windows/Fonts/Arial.ttf");
    sf::Text statsText("", font, 10);
    statsText.setFillColor(sf::Color::White);
    statsText.setOutlineColor(sf::Color::Black);
    statsText.setOutlineThickness(1);

    sf::RectangleShape rect;

    while(window.isOpen()) {
        sf::Event event;
        while (window.pollEvent(event)) {
            switch (event.type) {
                case sf::Event::Closed:
                    window.close();
                    break;
            }
        }
        statsText.setString(
            std::string("Draw Calls per Second: ") + std::to_string(window.getDrawCallsPerSecond()) + "\n" +
            std::string("Frames per Second: ") + std::to_string(window.getFramesPerSecond()) + "\n"
        );

        window.clear();
        for (unsigned int i = 0; i < 10; ++i)
            window.draw(rect);
        window.draw(statsText);
        window.display();
    }
    return 0;
}