How to Use This Calculator
1. Measure your tarantula's DLS. Diagonal leg span (DLS) is measured from the tip of one front leg to the tip of the opposite rear leg, with the legs outstretched as flat as possible. This is the standard sizing metric used by the keeper community.
2. Select the housing type. Choose Terrestrial for ground-dwelling or opportunistic burrowing species (e.g. Brachypelma, Grammostola, GBB); Fossorial for obligate deep-burrowers (e.g. Cyriopagopus lividus, Ornithoctonus aureotibialis); or Arboreal for tree-dwelling species (e.g. Avicularia, Poecilotheria, Psalmopoeus).
3. Enter feeder cost details to get a personalised monthly feeding cost estimate based on your actual prices and the recommended frequency for your spider's life stage.
All results update instantly. Use Print / Save as PDF to keep a record for your enclosure shopping list, or share the URL to reproduce your exact inputs.
Enclosure Sizing Formulas
The formulas used here reflect the most widely cited community standards from Arachnoboards, The Bio Dude, Spider Shoppe, and other recognised keeper resources. They represent minimum guidelines — more space is generally beneficial for juveniles and adults (slings often do better in slightly smaller enclosures for humidity stability).
Terrestrial (ground-dwelling)
Floor length (L): 3 × DLS (minimum), 4 × DLS (recommended)
Floor width (W): 2 × DLS (minimum)
Substrate depth: 1 × DLS
Max top clearance above substrate: 1.5 × DLS (to reduce fall injury risk)
Fossorial (obligate burrower)
Substrate depth: 2–4 × DLS (the more the better — fill 2/3 to 3/4 of enclosure)
Remaining headspace above substrate: ≥ 1.5 × DLS (water dish, anchor points)
Floor footprint: 2 × DLS per side (square-ish footprint is fine)
Arboreal (tree-dwelling)
Interior usable height: 3 × DLS (minimum), measured above substrate
Floor / width: 2 × DLS per side
Substrate depth: 2–3 inches for slings/juveniles; 1–2 inches for adults (for fall cushioning + humidity anchor only)
Prey Size & Feeding Frequency
A widely used rule from experienced keepers is that feeder insects should be no larger than the tarantula's carapace (prosoma) or abdomen (opisthosoma). The carapace is roughly 1/3 of the DLS measurement. Offering oversized prey increases the risk of injury during feeding and can cause the spider to gorge before premolt, triggering months of fasting.
- Spiderlings: every 2–4 days, pinhead-sized prey
- Juveniles: every 5–10 days, appropriately scaled prey
- Adults: every 7–21 days depending on species metabolism and abdomen fullness
Always remove uneaten feeders within 24 hours to reduce stress and injury risk, especially near molting. Stop feeding when the tarantula begins pre-molt preparation (sealing burrow, refusing food, laying a molt mat).
Guidance note: Results are minimum baselines derived from widely used keeper conventions, not official veterinary standards. Needs vary by species, age, individual behaviour, and room temperature. Always research your specific species' care sheet — and if in doubt, consult an experienced keeper or exotic invertebrate vet.
Frequently Asked Questions
How do you calculate the right enclosure size for a tarantula?
The widely used community standard is 3–4× the spider's DLS for floor length (terrestrials) or interior height (arboreals), and 2–4× DLS for substrate depth (fossorials). These are minimum safe dimensions. Slings often benefit from slightly smaller enclosures for microclimate stability, while adults thrive in the full recommended space.
What is diagonal leg span (DLS) in tarantulas?
DLS is measured from the tip of the front leg on one side to the tip of the rear leg on the opposite side, with all legs outstretched as straight as possible. It is the standard measurement used by hobbyists and breeders worldwide to describe spider size and to calculate appropriate housing dimensions.
How much substrate does a fossorial tarantula need?
Fossorial species like Cyriopagopus lividus (cobalt blue) and Ornithoctonus aureotibialis need 2–4× their DLS in substrate depth. For a 4-inch adult, that is at least 8–16 inches of substrate. Fill the enclosure 2/3 to 3/4 full so the spider can construct a full-length burrow and reinforce the opening with webbing at the surface.
How often should you feed a tarantula, and what size prey is safe?
Slings typically eat every 2–4 days; juveniles every 5–10 days; adults every 7–21 days. Prey should be no larger than the carapace — roughly 1/3 of the DLS. Feeding larger items increases the chance of injury and accelerates premolt, leading to long periods where the spider refuses food and stays hidden. Adjust frequency by observing the abdomen: a plump, well-rounded abdomen means the spider is well fed; a shrivelled abdomen means it needs food soon.
How much does it cost to feed a pet tarantula per month?
A single tarantula is extremely cheap to feed. Slings fed 2–3× per week may cost $1–$3/month. Adults fed one dubia roach or cricket weekly typically cost under $1/month. Keepers with large collections often maintain feeder colonies of dubia roaches or crickets, bringing per-spider costs close to zero. The cost scales simply: feeders per session × sessions per month × cost per feeder.
Can a tarantula enclosure be too large?
Yes. Oversized enclosures make prey difficult to locate, cause humidity to fluctuate more dramatically, and can stress the spider. This is especially true for spiderlings, which do best in tightly controlled micro-environments. Follow the 3–4× DLS guideline as a healthy balance between space and security, and size up only when the spider has grown past the halfway mark of the enclosure's floor width.