Provided herein, are droplet mixture compositions and systems and methods for forming mixtures of droplets. The system may comprise two or more droplet generation units. Each unit may include at least one first input well, a second input well, and an output well connected to the first and second input wells by channels that form a droplet generator. The combined droplet populations can be mixed, heated, and collected for multiple uses, such as for use as calibration standards for instrument testing and analysis.