How many gallons is my hot tub?

Measure inside the shell. Most 4 to 6 person spas hold 300 to 450 gallons, and every chemical dose depends on the number.

The accurate way: time the fill

Seats and moulded shells make measurements rough. Instead, time how long the hose takes to fill a 5 gallon (19 liter) bucket, then time the whole fill with the same hose and tap setting.

Why hot tub volume matters more than pool volume

A pool forgives a 20% error. A 400 gallon spa does not: the same teaspoon too many of dichlor pushes chlorine well past 10 ppm, and hot water plus a few bathers burns through sanitizer in hours. Get the number once, write it under the cover, and use it in the hot tub chlorine calculator.

Typical sizes

Two-person spas run 150 to 250 gallons. Four to five seats is usually 300 to 400 gallons. Six to seven seats is 400 to 550 gallons, and swim spas start around 1,500 gallons. The manufacturer's spec sheet lists it if you still have it, and the model number on the cabinet finds it.