Septic Tank Calculator

Q: How long should a drain field be?

Most residential drain fields are 100 to 300 linear feet, depending on soil percolation and home size. Sandy soil with fast drainage needs as little as 100 ft; clay or rocky soil needs 200 to 300 ft because water moves through it slowly. A perc test determines the exact length for your lot.

A septic system costs $3,000 to $30,000 installed, with most homeowners paying $5,000 to $15,000. A typical 1,000 gal tank with a 100 ft drain field in loam soil runs about $4,000 to $6,000 installed. Use the calculator to get tank, drain field, and permit costs for your soil and lot.

Estimated total—

Your system

Tank size (gallons) Drain field length

Unit

feetmeters

Soil type

SandyLoamClayRocky

Price assumptions

Tank ($/gallon installed) Drain field ($/ft) Permit + perc test ($)

Defaults & assumptions

Defaults: a 1,000 gal tank (3-bedroom home), 100 ft drain field, loam soil, and US national average rates. Adjust the tank size, drain field length, soil type, and rates above to match your project. The flat permit fee combines the building permit and the perc test (soil percolation test), which are required for any new installation.

Enter your tank size and drain field length above to see results.

Septic system installation cost

A septic system has three cost components. The tank itself runs $1,000 to $2,500 installed for a typical 1,000 gal concrete tank, the most common residential size. The drain field adds $1,500 to $5,000 depending on length and, more importantly, soil type: sandy soil is the cheapest at $10 to $15 per linear foot, rocky soil can run $25 to $40 per foot because it requires blasting or specialized excavation. Permits and the perc test add $500 to $2,000 on top, depending on jurisdiction. The wide range in total cost comes almost entirely from soil: a sandy lot with a 100 ft field runs $4,000 to $5,000, while a rocky lot with a 200 ft field can hit $20,000.

Typical septic system cost by size and soil (US averages, installed)
System	Materials only	Professionally installed
1,000 gal tank, 100 ft field, sandy soil	$2,500 to $3,500	$3,500 to $5,000
1,000 gal tank, 100 ft field, loam	$3,000 to $4,000	$4,000 to $6,000
1,250 gal tank, 150 ft field, clay	$5,500 to $7,500	$7,500 to $11,000
1,500 gal tank, 200 ft field, rocky	$11,000 to $15,000	$15,000 to $25,000

How the calculator works

Tank cost is gallons times the installed rate per gallon, which already includes the tank, delivery, and excavation to set it. Drain field cost is length times the per-foot rate. Picking a soil type prefills a typical rate (sandy $15, loam $18, clay $22.50, rocky $30 per foot) since harder soil means longer trenches and more fill material; edit the rate to match a real quote. Permit and perc test are a flat fee, since they don’t scale with size. The right tank size for your home is roughly 250 gal per bedroom plus a 250 gal reserve for daily flow. Price ranges reflect published US averages from national cost guides (Angi, HomeGuide, HomeAdvisor, 2026).

Septic tank cost FAQ

How much does a septic system cost?

A septic system costs $3,000 to $30,000 installed, with most homeowners paying $5,000 to $15,000. A typical 1,000 gallon tank with a 100 ft drain field in loam soil runs $4,000 to $6,000 installed. Rocky soil and longer drain fields push costs well past $15,000.

What size septic tank do I need?

A standard residential septic tank is sized by bedrooms: 750 gal for a 1 to 2 bedroom home, 1,000 gal for 3 bedrooms (the most common), 1,250 gal for 4 bedrooms, and 1,500 gal for 5 or more bedrooms. Local code may differ, so check with your county health department before sizing.

How long should a drain field be?

Most residential drain fields are 100 to 300 ft, depending on soil percolation and home size. Sandy soil with fast drainage needs as little as 100 ft; clay or rocky soil needs 200 ft to 300 ft because water moves through it slowly. A perc test determines the exact length for your lot.

Can you install a septic system yourself?

No. Septic installation requires a perc test (soil percolation test), a building permit, and a licensed installer in most US jurisdictions. The work also involves excavation, precise slope grading for the drain field, and inspection by the health department. DIY installations typically fail inspection and can contaminate groundwater, leading to fines and required removal.