Urban Agriculture (UA) is the widespread practice of food production within available city space using non-commercial, commercial and hybrid production technologies. The economic viability of UA remains a concern among UA practitioners. To investigate UA’s viability; land, labour and distribution cost are analyzed, and margin and benefit–cost ratio (BCR) under vacant lot, rooftop/backyard and discretionary labour UA are calculated. We present a straightforward approach to gauge the economic viability of UA taking examples from 40 distinct locations of two divergent development contexts of Adelaide, South Australia and Kathmandu Valley, Nepal. UA seems potentially viable by selecting high-value crops in Adelaide but showed little chance of viability under low-value crop scenarios in both contexts. The high cost of land is shown to be the primary driver of cost for UA. Labour cost appears to be a critical difference between the two cities, being an important constraint for the economic viability in Adelaide, where the wage rate is high. To improve economic viability, the respective governments and planners should consider better ways to avail subsidised land through policy intervention and volunteer or subsidised labour arrangement mechanisms. Home food gardens accessing available land and labour as a discretionary/spare time activity with zero distribution cost may represent the best way to produce food without exceeding market costs in cities.