Portable volumetric video capturing systems present a compelling alternative to traditional, bulky prototype systems used for streaming and interacting with volumetric content. Their key advantages, particularly flexibility and ease of deployment, make them suitable for a wide range of applications. However, despite their potential, there has been limited exploration into the design of such portable systems. This paper addresses this gap by conducting an in-depth analysis of portability and proposing an optimized camera array configuration tailored for high-quality volumetric content generation. Our approach begins with a novel, flexible camera calibration method that leverages geometric priors, enabling accurate alignment of multiple cameras without requiring specialized expertise. Building on this, we introduce a meticulous fusion technique that integrates captured and inferred data to reconstruct complete volumetric representations. This method achieves a fusion latency of less than 100 ms, ensuring real-time performance. We integrate these innovations into a portable capturing system, named PortaCap, which incorporates a carefully designed camera deployment strategy. Through both quantitative and qualitative evaluations, PortaCap demonstrates significant improvements in volumetric content quality, achieving enhancements ranging from 13% to 33.8%. These results underscore the system's potential to advance the state-of-the-art in portable volumetric video capture.