NAC 444 Septic System Design Calculator

Free NAC 444 Septic Leach-Field Calculator

Size a code-compliant absorption-trench leach field in seconds. This free NAC 444 septic design calculator from Thurston Laboratories, LLC applies the DPBH formula from its "Information for Individual Sewage Disposal System" handout, using NAC 444.8306 for tank capacity and NAC 444.8352-444.8356 for absorption-trench design. Enter bedrooms (or a custom tank size), your slowest percolation rate, and gravel depth under the distribution line to get total trench length, line count, and per-line length, plus a PDF report with the permitting checklist, setbacks, fees, and other details for your administrative authority.

Originally a command-line tool Dr. Thurston built for his clients, it now runs in the browser with the full DPBH checklist and defers to a licensed engineer when NAC 444 requires professional design. Homeowners, contractors, and design professionals all get the same conservative numbers in a white-label PDF with your company name, logo, and project metadata—no watermark, no charge, no license, no install.

1. Sizing source

Choose exactly one. The other field is disabled.

Use the NAC 444.8306 minimum tank size for the number of bedrooms. Specify a custom septic tank size in gallons.

2. Inputs

Number of bedrooms (NAC 444.8306)

Septic tank size (gallons)

Percolation rate (min/in, slowest of two test holes)

Gravel under distribution line (ft)

3. Report customization (optional)

Anything you fill in here is automatically applied to the white-label PDF report.

Report logo

Optional. The image is proportionally resized and printed in the top-left of every page of the white-label PDF report. Accepted formats: PNG, JPG, JPEG, GIF, WEBP. Maximum size: 2 MB.

No logo uploaded.

Business or firm name

Prepared by

Permit applicant

Property location (up to 3 lines)

Worked example: size a 3-bedroom system by hand

This walk-through mirrors the canonical example printed on the Nevada DPBH 'Information for Individual Sewage Disposal System' handout. Plug the same numbers into the calculator above and you will get the same answer.

Given

Single-family dwelling, 3 bedrooms.
Percolation rate (slowest of two test holes): 30 min/in.
Gravel beneath the distribution line: 2 ft.

Step 1 — Required septic tank capacity (NAC 444.8306)

A single-family dwelling with 3 or fewer bedrooms requires a septic tank with a minimum liquid capacity of 1,000 gallons.

Step 2 — Total leach-line length (DPBH formula)

Apply the DPBH absorption-trench sizing formula:

L_total = (TankSize) × (√perc / 5) / (2 × FtGravelUnderLine)

Step 3 — Plug in the numbers

With 1,000 gal, perc = 30 min/in, gravel = 2 ft:

L_total = (1000) × (√30 / 5) / (2 × 2) ≈ 273.86 ft

Step 4 — Round up and pick a line layout

Round 273.86 ft up to 274 ft. No perforated line may exceed 100 ft, and lines must be of equal length (DPBH handout; NAC 444.8354(3)). Three 92 ft lines give 276 ft of trench, which satisfies both constraints, so the design is 3 lines × 92 ft.

Step 5 — Distribution box

Any layout with more than one line requires a distribution box (DPBH handout). This design uses one.

Quick-reference sizing chart (1,000 gal tank)

Reproduced from the DPBH 'Information for Individual Sewage Disposal System' handout. Values in parentheses produce total trench lengths that exceed practical depth limits at 1 ft of gravel; cells marked — are not applicable at 4 ft of gravel for that percolation rate. Any total length over 500 lf requires a dosing tank and must be designed by an engineer (NAC 444.8326).

Perc rate (min/in)	1 ft	2 ft	3 ft	4 ft
10	316	158	106	80
15	387	194	129	97
20	447	224	149	—
25	500	250	167	—
30	(547)	273	182	—
35	(591)	296	197	—
40	(632)	316	210	—
45	(670)	335	224	—
50	(707)	353	235	—
55	(741)	370	247	—
60	(775)	387	258	—

Setback distances (DPBH handout)

Minimum horizontal distances in feet, reproduced verbatim from the DPBH 'Information for Individual Sewage Disposal System' handout. Verify every distance on the plot plan you submit with your permit application.

Distance from	Building Sewer Drain	Septic Tank	Disposal Field (Shallow)
Building or structure	—	8	8
Property lines	10	10	10
Water supply wells (sealed to 50 ft)	50	100	100
Water supply wells (NOT sealed to 50 ft)	50	100	150
Public water supply wells	50	150	150*
Streams or watercourses	50	100	100*
Drainage channels	25	25	25
Large trees or shrubs	—	10	10
Disposal fields	—	5	—
Community main water line	10	10	25
Individual water service line	10	10	25
Dry wells	—	6	20

* The required distance between a well and the components of an individual sewage disposal system may be increased by the health authority depending on the depth to the water table, soil profile, and other site characteristics.

Nevada DPBH fee schedule

Fees set by the State Division of Public and Behavioral Health for the areas it administers. Some Nevada counties administer NAC 444 through their own district or local administrative authorities with their own fee schedules (NAC 444.828, NAC 444.788(3)) — confirm with your local authority before submitting payment.

Item	Fee
Permit to construct an individual sewage disposal system for a single-family dwelling (plan review + initial inspection).	$498
Permit to construct a residential system using an alternative treatment or disposal system (plan review + initial inspection).	$498
Review of the plan for a primary treatment unit.	$498
Resubmission of or revision to any of the above plans, or tank-only replacements.	$124
Reinspection of an individual sewage disposal system.	$100
Extending a construction permit for a 1-year period after its expiration date.	$332

Permitting checklist

Tick each box as you complete it. The state is saved with your session and is reproduced verbatim in the PDF report so you can take it to your administrative authority.

Application submittal

Application form filled out and signed. (DPBH "Application and Design Plan Requirements")
Application fee paid by check or money order payable to "Division of Public and Behavioral Health" ($498 for a single-family-residence permit). (NAC 444.828)
One (1) copy of the design plan attached, containing every plot-plan item listed below. (NAC 444.784(3))
Local building department approval obtained (if required). (DPBH submittal checklist)
Percolation test data from at least two test holes, recorded on the NAC 444.797 sample form. (NAC 444.796 to 444.7968)
Soil profile log to a minimum depth of 5 ft below the bottom of the proposed absorption system. (NAC 444.835(3); NAC 444.7972)

Operational and inspection

Confirm the property is not within the service area of a public or community sewer (a permit will be denied if it is). (NAC 444.786(1)(b), (c))
Identify the administrative authority for your area (district health department, city, or county building inspector) and contact them before you begin. (NAC 444.788(3))
Confirm at least 4 ft of separation between the bottom of the disposal trench and seasonal high groundwater, impervious barriers, or other limiting soil characteristics. (NAC 444.835(6))
Verify every setback on the plot plan against the DPBH setback table (wells, watercourses, property lines, structures, etc.). (DPBH "Set Back Distances" table)
Schedule a pre-cover inspection with the administrative authority; do not backfill the trenches until the system has been inspected (or photographic documentation has been accepted at the authority's discretion). (NAC 444.788(1); NAC 444.8356(1))
Do not occupy the building or connect permanent electrical power until the individual sewage disposal system has passed inspection and an operating permit has been issued. (NAC 444.788(2))
Remember: the construction permit is valid for 1 year from issuance. A $332 extension fee applies if construction is not completed within that period. (NAC 444.786(6); NAC 444.828)

Saved state is included on every PDF report you generate.

Calculator FAQ

What is NAC 444 and why does it govern my septic system?

The Nevada Administrative Code (NAC) Chapter 444 contains the State Board of Health's rules for individual sewage disposal systems. NAC 444.750 to 444.8396 cover septic tanks, absorption trenches, alternative treatment units, dosing tanks, percolation testing, permits, and inspections. If you are building a single-family home outside a public sewer service area in Nevada, NAC 444 sets the floor for what your system must do.

Who can use this calculator?

Homeowners and licensed contractors designing a residential system for a single-family dwelling on soils with a percolation rate of 60 minutes per inch or less, free of limiting conditions such as high groundwater, sloping terrain, impervious soil, or bedrock (NAC 444.8352(3)). Engineers can also use it to spot-check a hand calculation. Commercial systems must be submitted to the Nevada Division of Environmental Protection for review (NAC 444.8302) and are out of scope.

When does my system have to be designed by an engineer?

NAC 444 requires engineered designs in several situations. The calculator refuses to release a sized result in any of them:

Percolation rate > 60 min/in (NAC 444.835(4); NAC 444.8354(9)).
Total absorption trench > 500 lineal feet: a dosing tank is required (NAC 444.8326(1)(d)) and a dosing-tank system must be designed by an engineer (NAC 444.8326(2)).
Commercial systems, regardless of size (NAC 444.8302).
Alternative absorption systems used because of limiting site conditions (NAC 444.8374).
Aerobic or nitrogen-removal treatment units (NAC 444.8316(3); NAC 444.8322(3)).

When do I need a distribution box?

The DPBH handout states that distribution boxes are required whenever more than 100 ft of total leach line is needed — in practice, any time the calculator returns more than one line. The results card flags this for you, and the PDF report includes a check-off in the permitting checklist.

What is the difference between a construction permit and an occupancy permit?

A construction permit authorizes you to install the system per the approved plan. It is valid for one year (NAC 444.786(6)). An occupancy permit is issued only after the installed system has passed inspection, the as-built plans and any well log have been submitted, and the administrative authority confirms the system is operating correctly. You cannot occupy the building or connect permanent electrical power until the occupancy permit has been issued (NAC 444.788(2)).

Do I still need a percolation test?

Yes. NAC 444.796(1) requires percolation tests from a minimum of two test holes in the area of the proposed soil absorption system. Use the slowest of the two rates in the calculator (NAC 444.835(11)). Record your results on the NAC 444.797 sample form and the NAC 444.7972 soil profile log, and include both with your permit application.

Is the calculator a substitute for an inspection?

No. The administrative authority must inspect (or accept photographic documentation of) the system before the trenches are covered (NAC 444.788(1); NAC 444.8356(1)). Cover the trenches before that inspection happens and you may be ordered to uncover them at your own expense.

References

NAC 444.784 — Permits: Approval for new construction; plot-plan contents.
NAC 444.786 — Permits: Denials, appeals, validity, and extensions.
NAC 444.788 — Inspections of individual sewage disposal systems.
NAC 444.796 to NAC 444.7968 — Percolation test: performance, procedures, sample form.
NAC 444.7972 — Sample log for profile of soil.
NAC 444.828 — Schedule of fees.
NAC 444.8306 — Capacity of septic tank serving single-family dwelling.
NAC 444.8326 — Dosing tank: General requirements (engineer-designed > 500 lf).
NAC 444.835 — Soil absorption system: General requirements.
NAC 444.8352 — Absorption trench system: General requirements; design calculations.
NAC 444.8354 — Absorption trench system: Design criteria.
NAC 444.8356 — Absorption trench system: Inspections.
STATE OF NEVADA DPBH handout — "Information for Individual Sewage Disposal System" (rev. 8/2014).