🦎 Reptile UVB Calculator

Select your reptile's Ferguson Zone and enter the basking-spot-to-lamp distance to see the recommended UVB lamp strength band. (A general reference lookup, not a precise measurement.)

Recommended T5 HO UVB Tube Strength

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Recommended Basking Distance Range for This Zone —

Important: actual UV output depends heavily on the specific bulb brand/model/age (UVB output degrades over months of use even if visible light looks fine) and enclosure factors (mesh screening blocks significant UVB). The only reliable way to confirm safe UV levels is to measure with a UV Index meter (e.g. a Solarmeter 6.5), and consult species-specific care sheets or a reptile veterinarian — this calculator is a starting-point reference only.

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GUIDE

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What Are Ferguson Zones?

Ferguson Zones are a widely adopted reptile-husbandry classification framework that groups species into four zones based on the ultraviolet (UV) exposure they experience in the wild. The system was originally proposed by Gary Ferguson and colleagues and popularized via UVGuide.co.uk.

Zone	Habitat Type (Examples)	UV Index	Recommended T5 HO UVB	Recommended Basking Distance
Zone 1	Shade dwellers/crepuscular (leopard gecko)	~0-0.7	2-6% UVB	30-45cm
Zone 2	Partial sun (many snakes, some geckos)	~0.7-1.0	5-6% UVB	25-35cm
Zone 3	Open/partial-sun baskers (juvenile bearded dragons)	~1.0-2.6	6-10% UVB	20-30cm
Zone 4	Full-sun baskers (adult bearded dragons, uromastyx)	~2.6-3.5+	10-14% UVB	15-25cm

The %UVB tube and distance bands above are approximate starting points commonly cited in reptile-keeping community references — they are not manufacturer-measured values for any specific bulb.

Why You Need a UV Meter and a Reptile Vet

This calculator's output is a general reference lookup, not a real-time-computed physical model. Actual UV output varies greatly with: (1) bulb brand and model — two tubes both labeled "10% UVB" can produce different real-world output; (2) bulb age — UVB output degrades significantly over months of use even when the visible light still looks fine, which is why regular replacement is needed; and (3) enclosure factors — mesh screening blocks a significant portion of UVB (often 30-50% or more depending on the mesh). The only reliable way to confirm safe UV levels is to measure at the basking spot with a UV Index meter (e.g. a Solarmeter 6.5), and to consult species-specific care sheets or a reptile veterinarian. Treat this calculator as a starting-point reference only.

Frequently asked questions

Can I rely on this calculator alone to set up my UVB lamp?

No. This calculator gives approximate starting points commonly cited in reptile-keeping references — individual animals and setups vary. Actual UV output depends heavily on bulb brand/model/age and mesh screening, so measure with a UV Index meter (e.g. a Solarmeter 6.5) and consult species-specific care sheets or a reptile veterinarian for advice specific to your pet.

Why do UVB bulbs need regular replacement?

UVB output degrades significantly over months of use even when the visible light looks fine. Follow the manufacturer's recommended replacement interval, and ideally verify actual output with a UV meter.

How do I know which Ferguson Zone my reptile belongs to?

Check species-specific care sheets or references such as UVGuide.co.uk. Note that the zone can differ by life stage even within one species (e.g. juvenile vs adult bearded dragons) — if unsure, consult a reptile veterinarian or an experienced breeder.