Water Softener Sizing Calculator

Only if you set Daily Water Usage to 0. Number of People is a fallback the calculator uses to estimate daily usage (at 75 gallons per person) when you haven't provided a direct usage figure; with the default Daily Water Usage of 300 gallons already entered, changing the number of people has zero effect on Required Grain Capacity, Recommended Softener Size, or any salt-usage output.

Dissolved iron adds to the resin bed's workload the same way hardness minerals do — each 1 PPM of iron is treated as equivalent to 5 additional grains per gallon of hardness in this calculator's Effective Hardness figure, which then flows into Required Grain Capacity. Water with even modest iron content (0.5-1 PPM) can meaningfully increase the recommended softener size compared to iron-free water of the same hardness.

Softener sizes come in fixed standard tiers (24,000, 32,000, 40,000, 48,000, 64,000, 80,000, and 96,000 grains), and the calculator recommends the smallest tier that covers your Required Grain Capacity — provided your Required Grain Capacity doesn't exceed the table's largest tier. A small change in hardness can leave your grain capacity within the same tier, so the recommended size stays put even though the underlying capacity requirement moved — it takes a big enough change to cross a tier boundary before the recommendation itself changes. If Exceeds Standard Sizing (1=Yes) is flagged, though, Recommended Softener Size is only the largest standard tier shown as a fallback, NOT a size that actually covers your load — high-hardness, high-usage, or long-regeneration-interval combinations (for example, 20 GPG hardness with 400 gallons/day usage and a 14-day regeneration interval, all individually within the declared input ranges) can silently exceed every tier in the table, so always check that flag before treating the recommendation as sufficient.

Salt usage is estimated from the resin volume implied by your Recommended Softener Size (about 8 lbs of salt per cubic foot of resin per regeneration), multiplied by how often the system regenerates per year (365 divided by Regeneration Interval), then converted to a monthly dollar figure using an assumed $6 per 40-lb bag. It's a planning estimate — actual salt cost varies with local pricing and your softener's specific regeneration settings.