Water Softener Sizing Guide

Water Softener Sizing

What size of softener do I need?

Water softeners are sized according to the grain capacity they are capable of removing between regenerations. A 48k or 48,000 grain system is capable of removing 48,000 grains of hardness between regenerations based on standard regeneration settings. To properly size a softener you will at minimum need to know your hardness level. If you are using an all-in-one system to treat iron and manganese you will need to know those levels as well. Knowing your typical water usage in gallons per month/week/day will also help get the most accurate recommendation, but averages can be used for that. Once you have that information follow the steps below to help determine what size of system you need. If you print this page off you can use the space to fill it out as you go.

Step 1
Determine water hardness level
Start with your water hardness (may be listed as CaCO3 on your water report). You will need the grains per gallon (GPG) level for these calculations. If your test shows parts per million (ppm) or milligrams per liter (mg/L) divide that by 17.1 to get the grains per gallon. (Round up to the nearest whole number for best results.)
Hardness (ppm or mg/L)

÷ 17.1 =
Hardness (in grains)

Step 2
Compensate for iron/manganese (if applicable)
If you have any iron or manganese (not to be confused with magnesium) in the water, add both of those together (in ppm or mg/l) and multiply by 4. Add that to the hardness from above to get your total compensated hardness. (Round up to the nearest whole number for best results.) If you do not have any iron or manganese enter 0 in that field, and your compensated hardness will be the same as your hardness above.
Iron (ppm or mg/L)

Manganese (ppm or mg/L)

Total Iron + Manganese

Iron + Manganese as Hardness

Hardness (from above)

Total Compensated Hardness

Step 3
Determine water usage (in gallons)
Determine how much water you use on average every day. You can either estimate your usage based on the number of people in the house, or you can take and divide the number of gallons used in a month as shown on a water bill or water meter. If you are unsure it is best to assume average water use for the number of people there the majority of the time. Our on demand softeners will adjust as necessary if there are more or less people than normal, but sizing should be made for normal circumstances to ensure the best results.
Number of people

Your water use (gallons per person per day)
Estimated water use (gallons per day)


Gallons shown on water bill

Average water use (gallons per day)

Step 4
Calculate daily and system grain requirements
Using the information calculated above, multiply your water usage (estimated or average) by your total compensated hardness. This will provide the average daily grains of hardness that you need to treat. Multiply that number by the number of days between regenereation desired to get your ideal grain capacity. With iron or manganese in the water 3-7 days is common (minimum of every 7 is recommended to prevent resin fouling). Water without iron or manganese are typically sized to go 7-14 days. Once you have your ideal grain capacity you can use it to find the system that most closely matches it.

NOTE ON SYSTEM CAPACITY: Water softeners are rated based on a maximum capacity using a high salt dosage. It is typically recommended to use a much lower (and more efficient) salt dosage, but this will also lower the available treatment capacity. If you want a more efficient system, most systems will operate at roughly 67% of stated capacity when using efficient salt settings (and use only 37% of the salt). You can use the "Efficient Grain Capacity" to see what rated size you will need to use efficient settings, or multiply the stated capacity of a system by 0.67 to get the efficient capacity.
Total Compensated Hardness (from above)

Water use (Estimated or Average from above)

Average Daily Grains

Days Between Regenerations
Ideal Grain Capacity

Efficient Grain Capacity

Final Thoughts & Recommendations
In most cases the system sizing recommended here will be adequate for most homes. If you have low hardness and/or a high flow rate (in gallons per minute) you may need to get a larger than recomended system to keep up with higher flow rate demand. Be sure to look at system service flow rates to ensure they meet your needs. If your ideal grain capacity is larger than our standard systems even using 3 days between regenerations you will want to use a dual tank system. You can also use a dual tank system if you want higher efficiency.

*PLEASE NOTE: This calculator is for reference only, and not intended to replace a full evalution of your water report by one of our experts.
Disclaimer: Abundant Flow Water is not resposible for any issues that may arise from purchasing a system based on this recommendation.
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