Mangrove forests are a globally important of reservoir of carbon (C). Consequently, interest in offsetting C emissions by buying “blue carbon” credits generated from mangrove restoration and conservation projects has burgeoned in the private sector. Belowground C, stored in roots and soils, cannot easily be remotely measured and is usually merely guessed at with global default values. If soils can be sampled, laboratory methods used to estimate C content are often either prohibitively expensive for practitioners or criticized as inaccurate by scientists. In this study, we compared both the accuracy and feasibility of commonly used methods to estimate soil organic C content, which is necessary to calculate soil carbon stocks converted into C credits. We analyzed soil samples collected from diverse locations throughout Senegal’s Saloum Delta. We found that the most simple and cost-effective method was just as accurate as the more expensive, complicated ones for determining C content. This finding could help increase accessibility of biogeochemistry research to under-resourced institutions. We also found very low C content in these semi-arid, sub-tropical mangroves. This means using conventional conversion factors almost doubled estimated soil C stocks, which would greatly over-inflate C crediting and enable status-quo climate-warming emissions.