calculee is a web-based laboratory tool designed to calculate solution dilutions and compound reconstitutions for scientific research. Its primary function is to solve the standard dilution equation, C1V1 equals C2V2, which determines the volume of a concentrated stock solution and the amount of diluent needed to reach a target working concentration. The tool also handles the reconstitution of lyophilized powders, using the compound mass and molecular weight to calculate the solvent volume required for a master stock. It is built as an alternative to the traditional Tocris Dilution Calculator, with automated handling of unit conversions and solvent ratios. The tool offers two main modes: single dilution and serial dilution. The single dilution mode takes an initial stock concentration, a final working concentration, and a final total volume, then calculates the required stock volume and diluent volume. The serial dilution mode generates multi-step dilution series, such as 2-fold, 5-fold, or 10-fold, across tubes or microplate wells. Additional features include metric unit normalization across molarity scales, including M, mM, µM, nM, and pM, and liquid volumes, including L, mL, and µL. The tool also computes the diluent volume directly as the difference between final volume and stock volume, and it provides guidance on solvent cytotoxicity prevention by helping users keep organic carriers like DMSO below the 0.1% ceiling for cell-based assays. Typical users include pharmacologists, biochemists, and life-science researchers who prepare working experimental solutions from concentrated stock vials. The workflow generally involves entering either the stock concentration or the desired final concentration, along with the target volume, and the tool returns the precise aliquot to pipette and the volume of buffer or media to add. For lyophilized compounds, the user enters the mass and molecular weight to determine the reconstitution volume. The tool also supports correcting for broad concentration intervals across different molarity and volume units, reducing the risk of stoichiometric calculation errors in both single and multi-step dilutions. The tool is freely available and can be accessed through a web browser. It does not require any specific software or hardware, and its interface is structured around the standard laboratory variables C1, V1, C2, and V2, making it suitable for both routine and complex dilution protocols. The underlying calculations rely on the conservation of mass principle, ensuring that the total amount of dissolved solute remains constant as solvent is added.