Home & Garden
Tools for working out how much of something you need, and guides for the part a number does not cover — what order to do things in, and when it is safe to get back in the water.
The questions a dose alone does not answer
Every figure in these is checked against CDC guidance and EPA-registered product labelling, with the sources listed on each page. They exist because getting the number right is only half of using a pool chemical correctly.
- How Much Muriatic Acid to Lower Pool pH? About 10 fl oz of 31.45% acid per 10,000 gallons lowers pH by roughly 0.2. Read the guide →
- Pool Shock Dosage Chart 1 lb of cal-hypo per 10,000 gallons; double for cloudy, triple for green. Read the guide →
- When Is It Safe to Swim After Shocking a Pool? When a test shows free chlorine at 4 ppm or below — not after a set number of hours. Read the guide →
Pool water chemistry
Dose it right, in the right order
Pool chemistry is a sequence rather than a set of independent numbers, and doing it out of order is how people end up chasing a reading all season. Volume comes first, because every dose on every other tool scales off gallons and an estimate here scales straight through. Then pH, because chlorine sanitises poorly above about 7.8 — a pool that will not hold chlorine often has a pH problem rather than a chlorine problem. Only then chlorine or shock. Alkalinity sits underneath all of it, governing how far a dose of acid actually moves the pH.
- Pool Volume Calculator Gallons from your pool shape and dimensions. Start here; everything else depends on it.
- Pool Chemical Calculator Chlorine, pH, alkalinity and stabiliser together, when more than one reading is off.
- Muriatic Acid Pool Calculator How much acid it takes to bring a high pH down.
- Pool Chlorine Calculator Routine chlorine dose for liquid, granular or bleach.
- Pool Shock Calculator The large one-off dose for cloudy or green water.
- Saltwater Pool Calculator Salt to add for a chlorine generator, and where the level should sit.
Before you add anything: never mix pool chemicals, and when pre-dissolving, add the chemical to water rather than water to the chemical — the reverse can react violently. Add one product at a time with the pump running, and test before anyone swims. The re-entry guide covers what to test for.
Buying materials by volume or area
How much to order, including the part you waste
These answer the same shape of question — how much of something covers an area or fills a space — and they share the same trap. What you order is not what the job consumes: paint soaks into porous surfaces, gravel settles, concrete is lost to spillage and uneven ground, and offcuts are rarely reusable. Each tool builds in the customary allowance rather than leaving you to remember one, and each rounds up to whole units, because that is how the shop sells it.
- Paint Calculator Litres or gallons by wall area, number of coats and surface type.
- Gravel Calculator Tonnes or cubic yards for a driveway or bed, by depth.
- Concrete / Mulch Volume Calculator Cubic yards for a slab, footing or mulch bed.
- Square Footage / Flooring Cost Calculator Total area across several rooms, and what covering it costs.
Around the house and garden
Getting the specification right, not just the quantity
Two jobs where the usual mistake is the wrong unit rather than the wrong number. Fertiliser is sold by weight but applied by nutrient content, so two bags with different N-P-K ratios need very different amounts spread over the same lawn. Bulbs are still bought on a wattage habit left over from incandescents, when the figure that actually determines brightness is lumens — an LED drawing a tenth of the power can produce the same light.
Every home & garden calculator
The complete list, for when you already know the tool you want.