Print material usage estimation

A method for determining an amount of print material in a print material reservoir, the method comprising:

• measuring a first weight of a spittoon or the print material reservoir;
• initiating a printhead maintenance event comprising ejecting print material into the spittoon;
• determining a number of drops fired during the printhead maintenance event using drop detection;
• measuring a second weight of the spittoon or the print material reservoir;
• calculating a representative drop weight based on the difference between the first weight and the second weight of the spittoon or the print material reservoir and the determined number of drops fired;
• and
• determining an amount of print material in the print material reservoir, based on the representative drop weight and a total number of drops fired.

A printer comprising:

• a spittoon to collect print material deposited by a plurality of nozzles during a printhead maintenance event;
• a weight sensor to measure a weight of the spittoon before the printhead maintenance event and after the printhead maintenance event;
• wherein
• the weight of the spittoon is used to calculate an amount of print material available in a print material reservoir.