Pool Borate Calculator: Borax or Boric Acid Dose
Dose borates from your pool volume, reading and target: pounds of boric acid, pentahydrate or laundry borax, the two halves to add them in, and the acid that holds pH.
How this is calculated
One mass balance, run on the boron content of whichever bag you actually bought. The ppm on a borate strip is boron measured as B, so the engine works on that basis and the answers line up with a strip reading.
pool_multiple = volume_gal / 10000
ppm_to_add = max(0, target_ppm − current_ppm)
boron_fraction = boron_pct / 100 x purity_pct / 100
ppm_per_lb_10k = boron_fraction x 11.9827
dose_lb = ppm_to_add / ppm_per_lb_10k x pool_multiple
per_dose_lb = dose_lb / 2 // the label splits it
Acid that holds pH (tetraborate routes only):
acid_fl_oz = dose_lb x fl_oz_per_lb x (31.45 / your_acid_pct)
dry_acid_lb = dose_lb x lb_per_lbWorked example. A 10,000 gallon pool at 0 ppm, taken to 50 ppm on the pentahydrate. Boron content is 14.845%, so one pound is worth 1.779 ppm per 10,000 gallons and the pool needs 28.11 lb, which is 12.75 kg, going in as two halves of 14.05 lb. At the label ratio that calls for 281 fl oz of 31.45% muriatic acid, about 2.2 gallons, or 21.08 lb of dry acid. The same 50 ppm on boric acid is 23.86 lb and no acid at all; on laundry-aisle borax it is 36.8 lb and the same 281 fl oz of acid, because acid demand follows moles of tetraborate rather than pounds of bag.
Where the boron contents come from. Manufacturer product data sheets, cross-checked against the molecular weights printed on those same sheets with boron's atomic mass of 10.811:
- Boric acid, H₃BO₃. U.S. Borax Optibor data sheet: molecular weight 61.83, theoretical composition 56.30% B₂O₃. Boron is 10.811 / 61.83 = 17.485%, and 56.30% × 0.31057 gives 17.486%. Both routes agree.
- Sodium tetraborate pentahydrate, Na₂B₄O₇·5H₂O. U.S. Borax Neobor data sheet: molecular weight 291.30, 47.80% B₂O₃. Boron is 4 × 10.811 / 291.30 = 14.845%, and 47.80% × 0.31057 gives 14.846%.
- Sodium tetraborate decahydrate, Na₂B₄O₇·10H₂O, the borax in the laundry aisle. U.S. Borax borax decahydrate data sheet: molecular weight 381.37, so boron is 4 × 10.811 / 381.37 = 11.340%.
Why one pound is 11.98 ppm. Water weighs 8.3454 lb per US gallon, so 10,000 gallons weigh 83,454 lb and one pound of pure substance in it is 11.98 parts per million. Multiply by the boron fraction and you get 2.095 ppm per lb per 10,000 gallons for boric acid, 1.779 for the pentahydrate and 1.359 for the decahydrate. The same 8.3454 figure is the reciprocal of the constant the rest of the pool tools on this site run on.
The label cross-check. ProTeam Supreme (sodium tetraborate pentahydrate 100.0%), EPA Reg. No. 57787-27, master label stamped 29 September 2016 in the EPA Pesticide Product Label System, directs two pounds per 1,000 gallons for the initial application and a residual "maintained at 30-50 ppm". Two pounds per 1,000 gallons is 20 lb per 10,000 gallons, which this engine puts at 35.6 ppm: inside the label's own band. That agreement is the check that the arithmetic above is written on the same basis the label is.
The acid figures. From the same label: "For initial pH adjustment use ¾ pound ProTeam pH Down (Sodium Bisulfate) or 10 ounces of muriatic acid for each pound of ProTeam Supreme, mixing acid in a bucket of water, then add to pool." The label writes that acid figure as bare ounces; this page reads it as fluid ounces, which is the reading the stoichiometry below supports. Those two numbers are the pentahydrate constants. The decahydrate figures, 7.64 fl oz and 0.573 lb per pound, are derived from them by molar ratio (291.30 / 381.37), because acid demand follows moles of tetraborate, and they are labelled as derived rather than as label figures. Both agree with the stoichiometry, which needs 2 mol of hydrochloric acid per mol of tetraborate: 10.5 fl oz of 31.45% acid per pound of pentahydrate and 8.0 per pound of decahydrate. The acid figures are stated at 31.45%, the same reference strength the muriatic acid dose calculator uses, and scale inversely with the strength of the jug you are holding.
What the tool will not do. It will not invent a dose that lowers borates, because none exists: the label states the product is lost only through filter backwash and splash-out. It will not push a reading that is already in band toward the middle of it. And it will not predict the pH landing point, only the acid the label pairs with the dose, because how far pH actually moves depends on the water's alkalinity.
Sources: U.S. EPA Pesticide Product Label System, EPA Reg. No. 57787-27 ProTeam Supreme master label, stamped 29 September 2016 (active ingredient, the two pounds per 1,000 gallons initial rate, the split into two applications, the 30 to 50 ppm residual band, the pH rise, the acid pairing, and the backwash and splash-out loss route). U.S. Borax product data sheets for Optibor boric acid, Neobor borax pentahydrate and borax decahydrate (molecular weights and theoretical B₂O₃ composition). Volume converts with 1 US gallon = 3.785411784 L, and 1 fl oz = 29.5735295625 mL.
What a pool borate calculator works out
Borates are dosed once, in bulk, and the amount depends on which bag you bought. Per 10,000 gallons, taking a pool from zero to 50 ppm needs about 23.9 lb of boric acid, 28.1 lb of sodium tetraborate pentahydrate or 36.8 lb of the decahydrate sold as laundry borax. Enter your volume, your strip reading and your target above and the tool prints the pounds and kilogrammes, splits them into the two applications the label directs, and sizes the acid the tetraborate route needs to hold pH.
Every figure is a pure function of what you typed this session. Nothing is saved, there is no pool profile and no account, and the label on the bag is the authority on everything the page does not compute.
Three products, three boron contents
The reason a borate calculator cannot have one constant is that “borate” names a family, not a product. What the strip reads is boron, and what varies is how much boron a pound of each product carries:
| Product | Formula | Boron content | ppm per lb per 10,000 gal | To 50 ppm per 10,000 gal |
|---|---|---|---|---|
| Boric acid | H₃BO₃ | 17.485% | 2.095 | 23.9 lb |
| Sodium tetraborate pentahydrate | Na₂B₄O₇·5H₂O | 14.845% | 1.779 | 28.1 lb |
| Sodium tetraborate decahydrate (borax) | Na₂B₄O₇·10H₂O | 11.340% | 1.359 | 36.8 lb |
Those boron contents are not rules of thumb. They come off the U.S. Borax product data sheets for Optibor, Neobor and borax decahydrate, and each one checks out twice: from the theoretical B₂O₃ composition on the sheet, and independently from the molecular weight on the same sheet against boron’s atomic mass of 10.811. The two routes agree to three decimal places. The remaining constant is arithmetic: water weighs 8.3454 lb per US gallon, so 10,000 gallons weigh 83,454 lb and one pound of pure product in it is 11.98 ppm.
The check that matters is against a real label. ProTeam Supreme (sodium tetraborate pentahydrate, EPA Reg. No. 57787-27) directs two pounds per 1,000 gallons for the initial application, which is 20 lb per 10,000 gallons. Run that through the table above and it lands at 35.6 ppm, inside the label’s own 30 to 50 ppm band. The arithmetic and the label are written on the same basis.
The coupled side effect: borates need acid to hold pH
Sodium tetraborate is alkaline. The label does not hide it: “the pH of the pool water may rise as a normal reaction to the introduction of ProTeam Supreme”, and it pairs the dose with a correction of 10 ounces of muriatic acid, or three quarters of a pound of dry acid (sodium bisulfate), for each pound of product, “mixing acid in a bucket of water, then add to pool”. On a 10,000 gallon pool going to 50 ppm that is around 281 fluid ounces of 31.45% acid, about 2.2 gallons. It is not a footnote; it is a second purchase and a second handling job on the same visit.
The tool scales that correction to your dose and to the strength of the jug you actually have, because a 14.5% acid needs more than twice the volume of a 31.45% one. For the decahydrate the per-pound figures are derived from the label’s by molar ratio rather than printed, because acid demand follows moles of tetraborate rather than pounds of bag, and the page labels them as derived. Both agree with the stoichiometry, which needs two moles of hydrochloric acid per mole of tetraborate.
Two consequences follow. The acid pulls total alkalinity down as well as pH, which is what the total alkalinity calculator reads back; and if you would rather size the acid on its own readings than on a pound count, the muriatic acid dose calculator takes a pH and an alkalinity figure instead.
Boric acid trades the problem the other way. It is mildly acidic in solution, so it needs no acid alongside it and nudges pH down slightly, and it carries the most boron per pound of the three. What it costs is price per pound, and its own label carries its own handling terms.
Nothing takes borates back out
The label is blunt about the exit route: the product is “lost from water only through filter backwash and splash-out”. That is the whole reason to get the target right the first time. There is no chemical that lowers borates, so a pool dosed to 80 ppm stays near 80 ppm until enough water has left and been replaced. When your reading is already above your target, the tool says so and prints no dose rather than inventing one.
Where this sits in the visit
Borates are a buffer, not a sanitiser. They hold pH steady against the acid demand of the rest of the chemistry and suppress algae alongside chlorine, and the label requires an EPA registered sanitizer to be used with them. The label also sets the shape of the treatment itself: the initial application is directed to go in as two equal doses rather than one, and the pH is to be adjusted after a normal turnover of pool water, which is why the tool prints the dose already halved.
The rest of that sequence, chlorine through pH, alkalinity, calcium, stabilizer and salt, is on the pool chemical dosing calculator, which has no borate line at all. That is why this page exists. If you do not know the pool’s volume, which every figure here is scaled by, start at the pool volume calculator.
What it is not
It is a quantity estimate, not a water-safety record and not a substitute for the product label. The bag you bought carries the strengths, the handling terms and the warnings that govern its use, and they win over any figure on this page. Borate products are dosed to a residual you test monthly, so treat the dose as the opening move and the strip as the authority. Print the treatment as a poolside worksheet, or export CSV, PDF or copy as text, all ungated and without an account.
Frequently asked questions
How much borax do I need to raise my pool to 50 ppm borates?
Do borates raise pH?
What is the right borate level for a pool?
How do I lower borates in a pool?
Does the calculator work in litres and kilograms?
Sources
- EPA Reg. No. 57787-27, ProTeam Supreme master label: sodium tetraborate pentahydrate 100.0%, two pounds per 1,000 gallons for the initial application added in two equal doses, a residual maintained at 30 to 50 ppm, the pH rise it causes, the pairing of 3/4 lb of dry acid or 10 ounces of muriatic acid per pound of product, and loss only through filter backwash and splash-out. U.S. EPA Pesticide Product Label System (master label stamped 29 September 2016). Retrieved .
- Optibor boric acid product data sheet: molecular weight 61.83, theoretical composition 56.30% B2O3, mildly acidic in solution. U.S. Borax (product data sheet 8/2026). Retrieved .
- Neobor borax pentahydrate product data sheet: molecular weight 291.30, theoretical composition 47.80% B2O3, mildly alkaline in solution. U.S. Borax (product data sheet 6/2025). Retrieved .
- Borax decahydrate product data sheet: molecular weight 381.37, the laundry-aisle borax. U.S. Borax (product data sheet 9/2024). Retrieved .