How Much Substrate Do I Need?

Last updated: November 29, 2025

The purpose of this tool

There are many options for tarantula substrate. Some people, especially people with a lot of tarantulas, choose to make their own substrate mix. There are also many pre-made options available.

The point of this tool isn't to help you decide which substrate to use, but rather to help you figure out how much you need if you decide to go with pre-made options.

Some substrate options may contain affiliate links, which help support the site at no additional cost to you.

To use this tool, simply enter the floor dimensions of your enclosure, as well as the substrate depth you want to fill, and click "add." You can add multiple enclosures to figure out the total amount of substrate you need. Simply select which substrate you prefer from the drop-down, and the tool will tell you how many bags you need.

Substrate Calculator

FAQs

Should I make my own substrate, or buy something pre-made?

This is a question that depends a lot on the individual. If you only keep a few spiders, buying pre-made makes a lot of sense. If you have a lot of spiders, you can definitely save money by making your own substrate, but may still choose pre-made for ease of use.

Which substrate is best?

This is something I have trouble answering. Tons of tarantula keepers use different substrates and are able to raise healthy spiders. There isn't a single best substrate, but you will want something that can hold a burrow and hold some moisture if needed. Any of the pre-made options in the tool will do that, so it is really just personal preference.

How do I know how much substrate to buy?

That is the exact purpose of this tool. In short, you need to calculate the volume of space you want to fill with substrate, and compare that to the volume of the bags. The tool on this page does that for you.