Ireland offers a complete testing pathway for wave energy devices from small-scale testing in laboratory wave tanks to the Galway Bay Test Site (GBTS), located in a sheltered bay, and the full-scale Atlantic Marine Energy Test Site (AMETS) exposed to the Atlantic Ocean on its west coast. This research investigates the scaling relationships between the GBTS and the AMETS, and also with the Westwave commercial demonstration site. The paper presents (i) detailed wave resource assessments at GBTS and Westwave (ii) a scaling analysis methodology suitable for determining the scale relationships between two sites, and (iii) the appropriate scaling factors for wave energy test sites in Ireland which can be used by developers for prototype testing and commercial deployment. The assessment and scaling analyses were performed using 12-year model outputs from two high resolution wave models from January 2004–December 2015. The models were well-validated using available measured data. The resource assessments determined (1) mean and maximum conditions and (2) operational, high and extreme event conditions for significant wave height, energy period and power. Both annual and seasonal analyses are presented. The 12-year annual mean power was 3 kW/m at GBTS and 50 kW/m at Westwave. Three scaling approaches have been analysed to identify the appropriate scale ratios to be used to upscale GBTS to AMETS for wave height, energy period and power. The distribution fittings method was found to be the most accurate method for resource scalability between GBTS and both AMETS and Westwave sites. The scaling result shows GBTS, although often termed a ¼-scale test site, is not actually ¼-scale proportionate to AMETS or Wavewave. Scaling factors are presented in tabular format, which are based on the Froude scaling method, for seasonal windows that could be used to determine the scale of ocean energy device models for testing in the benign site of GBTS in Ireland to ensure it adequately upscales to the open sea exposed sites of AMETS and Westwave in Ireland.