Abstract <p>The comparison of satellite and visual cloud cover observations over the ocean is a crucial aspect of modern climatology and meteorology. Since 1853, visual cloud observations have been systematically conducted from commercial vessels, forming the basis of the extensive ICOADS dataset, which contains millions of ship-based meteorological reports distributed across the world’s oceans. Initially, cloud cover was measured in quarters of sky coverage, later transitioning to a ten-point scale in the first half of the 20th century. Since the 1950s, the eight-point scale (okta) has become the standard, where eight oktas represent complete cloud cover. The advent of satellite technology in the 1970s revolutionized cloud cover monitoring. Geostationary satellites like METEOSAT provide high-resolution data (0.05° × 0.05°) with multiple hourly images, while polar-orbiting satellites such as EPS/MetOP and POES/NOAA complement these observations. Comparing satellite and visual data presents two major challenges. First, visual observations cover approximately a 13–14 km radius from a height of 12–13 m, requiring proper spatial averaging of satellite data. Second, conversion between measurement units—from okta to percentage coverage—demands careful consideration. The study analyzed two primary datasets: ICOADS visual observations and COMET ed. 2.0 satellite data from 1983 to 2021 in the North Atlantic region. The research methodology included spatial averaging of satellite data, quality control of visual observations, daytime filtering, and exclusion of night observations due to lower accuracy. Analysis revealed several significant findings. Visual observers tend to underestimate cloud cover, sometimes by more than two oktas. Daytime observations showed higher accuracy than nighttime measurements. The research established clear thresholds: values below 6.25% correspond to clear sky (0 oktas), while values above 93.75% indicate complete cloud cover (8 oktas). This comparative analysis provides a reliable method for correlating visual and satellite cloud cover observations. The developed conversion scale enhances the accuracy of cloud cover assessments over the ocean. Future research should extend this methodology to other ocean regions, considering regional observational practices and climatic characteristics. The study emphasizes the importance of combining different observation methods to improve our understanding of cloud cover dynamics and its impact on Earth’s climate system. Regional differences in observational practices, vessel-specific observation heights, and national variations in maritime observation techniques all play significant roles in data accuracy and interpretation.</p>