With the increase in greenhouse gas emissions after the industrial revolution, global warming has become a worldwide concern. The creation of the carbon market, stemming from the Kyoto Protocol, raised interest in carbon, as it is one of the main contributors to this effect. It is necessary to increase knowledge about organic matter (OM), as it is composed of 58% carbon. Due to the high costs and generation of chemical waste for carbon chemical evaluation, new methods such as spectrometry, which do not generate waste and provide instant results, have become necessary. The objective of this study was to evaluate composting through spectrometry and, consequently, determine the behavior of the composting phases' spectra and in quantities measured with sand. The composting experiment was conducted at SIPA - Fazendinha Agrobiológica, and the spectral analyses were performed at the Geoprocessing Laboratory of UFRRJ. Chemical analyses were carried out on the compost to verify compliance with current legislation, which showed good quality parameters. In the spectral analyses, principal component analyses were performed with raw data and pre-processed data using SNV, SMO, MSC, and SGD1 in the RGB and IV regions, followed by multivariate calibration using PCR and PLSR. The principal component analysis proved capable of separating the composting phases and was also quite effective in separating the sand from sand with measured amounts of organic matter. It was possible to identify the ideal wavelengths for such separations. For multivariate calibration, PCR proved to be more effective in validating the data obtained by PCA.