Spa Switch
Hot Tub Chlorine Calculator for Dichlor and Liquid Chlorine
Spa Switch
Free web calculator. Native app for saved history.
Calculate today's dichlor or liquid chlorine dose below. If you want saved profiles, CYA switch tracking, refill history, pH and alkalinity trends, presets, and CSV export, use the iPhone app.
Free web calculator
Calculate a hot tub chlorine dose
FC rise
2.5 ppm
Dose
0.25 oz by weight
CYA from dose
2.25 ppm
This calculator uses the same public constants as Spa Switch. Always follow chemical labels and your hot tub manufacturer's guidance.
Save the dose when you want history
The web calculator is for a quick one-off dose. The optional lifetime unlock in Spa Switch adds local history, accumulated CYA since refill, switch-state tracking, pH and alkalinity trend logging, soak-load presets, refill reset, and CSV export.
Spa Switch does not certify water safety, replace chemical labels, or replace manufacturer guidance. It uses the values you enter.
Download Spa Switch
What the calculator supports
Dichlor mode
Calculate dose by weight and see the projected CYA increase from the current dose.
Liquid chlorine mode
Calculate fluid-ounce dose without adding CYA to the refill-cycle log.
Guides
FAQ
Is the chlorine calculator free?
Yes. The current-dose calculator is free. Paid unlock adds local history and advanced tracking.
Does this app tell me if my water is safe?
No. It is a calculator and log. You still need your own test results, product labels, and manufacturer guidance.
Can I track when to switch from dichlor to liquid chlorine?
Yes. After unlock, logged dichlor doses accumulate CYA and show switch-state status relative to your threshold.