A saltwater pool needs salt at a target ppm. Pounds to add = the ppm shortfall times volume, scaled by a constant — only when current salt is below target.
The example
20,000 gal, 3,200 → 3,200 target.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | (3200−2700)×20000/120000 | — |
| 3 | Salt to add | → ~83 lb |
The formula
The formula:
How it works
How it works:
- Find the ppm shortfall = target − current; MAX(…, 0) — you can’t remove salt by adding.
- Multiply by gallons and divide by the constant (~120,000 for lb/ppm).
- Convert to bags with ROUNDUP(pounds ÷ 40).
- If over target, the only fix is dilution — partial drain and refill.
Educational use only — not chemical-safety or professional advice. Pool chemical dosing varies by product strength, water chemistry, and local rules. Always follow the product label, add chemicals to water (never water to chemical), test before and after, and never mix chemicals. Verify with a professional.
Try it: interactive demo
Gallons, current ppm, target ppm.
Variations
Bags (40 lb)
Round up:
Over target?
Dilution needed:
Dilution fraction
Drain & refill share:
Pitfalls & errors
Floor at zero. Adding salt can only raise ppm — MAX.
Constant varies. ~120,000 for pounds; confirm your unit.
Over target = dilute. The only way down is drain and refill.
Practice workbook
Frequently asked questions
How do I calculate salt to add to a pool in Excel?
How many 40-lb bags is that?
What if salt is over target?
Stop fighting formulas. Learn them in a day.
This recipe is one of hundreds of real-world formulas we teach. Our Excel Formulas & Functions class covers lookups, logic, text, and dynamic arrays hands-on — live in Dallas–Fort Worth, Houston, Austin, Oklahoma City, Denver, or online.
See the Formulas & Functions Class