Keeping rhinoceros or stag beetles costs most in fermented substrate, bought again and again. One fill is easy enough to measure from the enclosure, but the figure that matters is how many bags a year ends up being. Give this page the inside length and width, the substrate depth you fill to, how many enclosures you run, your bag size and your change interval, and it returns both the per-change and the yearly amount.
Volume is length times width times depth, divided by 67.2 to convert cubic inches to US dry quarts, the unit substrate bags are sold in (1 dry quart = 1.101221 liters; liters are shown alongside). Enter the bag size in dry quarts as printed on the bag. Changes per year are 365 divided by the interval, rounded up, since the leftover part of the year still needs one more fresh fill (a 53-day interval gives 365 ÷ 53 = 6.9, counted as 7), and the yearly amount is the per-change total multiplied by that count. Bags are rounded up only once at the very end rather than at each step, so the count does not inflate. The table compares how the yearly amount shifts as the change interval changes.
Keeping temperature, humidity and substrate change intervals are not published by an official source. Interval and bag size are therefore yours to enter; the page proposes no feeding, temperature or humidity figures and does not deal with stocking density by larva count. How firmly the substrate is packed shifts the real requirement. Current as of October 2026.
Frequently Asked Questions
No official value is published, so enter the interval you already work to. Comparing the yearly amounts in the table makes that choice easier.
No. Enter the depth of substrate you actually fill, not the height of the box. Empty space above the substrate does not count toward the volume.
Because rounding up happens once at the end. Rounding at every change and then adding would inflate the number of bags.