Home Pool Borate Calculator
Pool Borate Calculator — Borax & Boric Acid Dosing
Estimate a reference amount of boric acid, borax, or sodium tetraborate pentahydrate from your pool volume, current borate reading and target borate level. The calculations are based on PHTA example chemistry expressed as ppm boron.
Last reviewed: October 5, 2026 · How we verify calculations and sources
💡 Borates are measured as boron, and the product matters
Boric acid, laundry-type borax (decahydrate), and sodium tetraborate pentahydrate contain different amounts of boron by weight. PHTA's example calculations therefore use different pounds for the same ppm increase. Commercial product purity and label directions still take precedence.
Calculate boric acid or borax for your pool
Compare the exact borate product before you dose
Boric acid, borax and pentahydrate are not interchangeable pound-for-pound. Confirm the ingredient on the product you buy, and test the starting borate level if the pool may already contain borates.
Borate dosing reference — why the amounts differ
PHTA's borate technical note gives example amounts needed to add 10 ppm as boron to 10,000 gallons. Those examples are the calculation basis used here:
| Borate source | Reference amount for +10 ppm / 10,000 gal | Approx. amount for +50 ppm / 10,000 gal |
|---|---|---|
| Boric acid | 4.57 lb | 22.85 lb |
| Borax (decahydrate) | 7.05 lb | 35.25 lb |
| Sodium tetraborate pentahydrate | 5.39 lb | 26.95 lb |
Those are reference-chemistry values, not permission to ignore a commercial label. For example, a current Pro Series boric-acid product states that 1 lb in 10,000 gallons adds approximately 2 ppm and specifies a 30–35 ppm maintenance range—close to, but not identical with, a pure-chemistry conversion.
Pool borate calculator formula
The calculator scales the PHTA reference amount by both pool size and the ppm increase:
Pounds needed = reference lb × (pool gallons ÷ 10,000) × (target ppm − current ppm) ÷ 10
Worked example — boric acid
A 15,000 gallon pool going from 10 ppm to 40 ppm needs a 30 ppm increase. Using the 4.57 lb boric-acid reference: 4.57 × 1.5 × 3 = 20.57 lb. Before dosing, compare that reference result with the actual boric-acid product label and purity.
Borax vs boric acid for pools
The two names are often treated as interchangeable in pool discussions, but the dosing and pH effects are not the same.
⚗️ Boric acid
Contains more boron per pound than borax decahydrate, so less product is required for the same ppm increase. It is also the option that avoids the large upward pH push associated with sodium tetraborate products.
📦 Borax (decahydrate)
Laundry-type sodium tetraborate decahydrate contains less boron per pound, so the dose is larger. It is alkaline and can raise pool pH significantly.
🧪 Pentahydrate
Sodium tetraborate pentahydrate contains more boron per pound than decahydrate, so its required mass sits between boric acid and laundry-type borax. It can also raise pH.
🏷️ Commercial products
Pool products may specify purity, a maintenance range and an application method. If the label rate differs from the generic chemistry estimate, use the label.
Why this calculator does not auto-dose acid with borax
Borax and other sodium tetraborates can raise pH, so some dosing recipes pair them with muriatic acid. A fixed acid-per-pound shortcut can look convenient, but it hides variables that this site normally treats explicitly: starting pH, total alkalinity, acid strength and product formulation.
For that reason, this calculator estimates the borate product only. Follow the borate product's application directions, allow the water to circulate, retest pH and TA, then use the pH Calculator or Muriatic Acid Calculator if a correction is actually needed. Never mix concentrated acid directly with borax, chlorine or another pool chemical.
Before adding borates to a pool
Borates are an optional water-treatment choice, not a substitute for basic sanitation and water balance. Before a large addition, verify the pool volume and starting borate level so you are not dosing from an assumption.
- Measure first. If the pool has ever received a borate product, do not assume the current level is zero.
- Confirm the ingredient. Boric acid, sodium tetraborate decahydrate and pentahydrate are not dosed pound-for-pound.
- Use the product's target range. PHTA describes a common 30–50 ppm range as boron, but a commercial product can specify a narrower range.
- Keep sanitizer management separate. Continue maintaining the chlorine or sanitizer residual required for your pool.
- Retest after circulation. Large additions are easier to correct when you verify the result before topping up.
Pool borate calculator FAQs
How much borax do I need for a pool?
It depends on pool volume, current borates, target borates and the exact borate chemical. PHTA example chemistry uses about 7.05 lb of borax decahydrate per 10,000 gallons for each 10 ppm increase as boron. Use the calculator for your measured starting level and target, then confirm the product label and ingredients.
How much boric acid raises borates by 10 ppm?
PHTA example calculations use about 4.57 lb of boric acid per 10,000 gallons to add 10 ppm as boron. Commercial products can have different purity and labeled application rates, so their label takes precedence over a generic chemistry estimate.
What borate level should I target in a pool?
PHTA technical guidance describes a common 30–50 ppm range measured as boron and says 50 ppm should not be exceeded. Some commercial boric-acid products specify a narrower maintenance range, so use the range on the product you actually use.
Does borax raise pool pH?
Yes. Sodium tetraborate products are alkaline and can raise pH. This calculator does not automatically pair borax with a fixed acid dose because the required pH correction depends on total alkalinity, starting pH, acid strength and the product directions. Retest first, then use a TA-aware pH calculation if needed.
Is boric acid the same as borax for pool dosing?
No. Both can supply boron, but they contain different percentages of boron by weight and have different effects on pH. That is why the calculator uses a different reference factor for boric acid, borax decahydrate and sodium tetraborate pentahydrate.
Can borates replace chlorine?
No. Borates are not a replacement for the sanitizer residual required for pool operation. Continue testing and maintaining chlorine or the sanitizer system appropriate to your pool.
How do I lower borates if the level is already above my target?
This calculator does not calculate a chemical borate reducer. If you need to lower a dissolved concentration, water replacement changes the concentration proportionally; use the Pool Dilution Calculator to estimate that effect and follow any applicable discharge restrictions.