Tile depth and spacing calculator
Pick a soil texture or enter what you know about the soil, and get a starting range for drain depth, then the depth a lateral needs at each spacing. For early planning and conversations, never for installing.
This calculator gives rough, generic estimates from a textbook equation and typical soil values. It is not a drainage design and not engineering, agronomic or legal advice. Results for your field can be wrong by a wide margin, in either direction.
Never install, quote or buy materials from these numbers alone. Confirm the soil with a site investigation, check local drainage guides and regulations, and have the system designed by a qualified drainage professional.
1. The soil
Use the soil at and just above drain depth: the tightest layer there controls how fast water reaches the tile.
2. The site (optional: defaults shown)
Leave these as they are if you are not sure.
3. Estimates
Why the worked spacing can differ from the guide range
The guide range comes from experience in the field. It is the published table range for soils like this one, drawn from drains that were installed and performed. It quietly includes things a single number cannot: cracks, root and worm channels and soil structure that let water reach the tile faster, and fields that tolerate a water table sitting high for a day or two after a big rain.
The worked spacing comes from one equation. Hooghoudt's equation assumes one uniform soil with one Ksat from the surface to well below the drain, rain arriving steadily at the drainage coefficient, and a water table never allowed above your target midway between drains. It is strict, and it is only as good as the Ksat you give it.
- Worked spacing below the range, which is common in clays and clay loams: the Ksat that fits the texture is low, so the equation asks for close drains. Many clays drain faster in the field through cracks and channels than that Ksat suggests, which is why the published ranges are wider. It can also mean the soil really is that tight.
- Worked spacing above the range, which is common in loams and sandy soils: the equation sees a fast soil and allows wide drains. Guides stay narrower on purpose, to allow for layers, compaction, variable soils and wetter years.
Neither number is a design. A wide gap between them is itself the useful answer: it says this soil needs a measured Ksat, local guidance and a drainage professional before anyone picks a spacing.
Drain depth at each spacing
The depth a lateral would need for the water table to fall to your target midway between drains, at the drainage coefficient above.
| Lateral spacing | Drain depth | Compared with the depth range |
|---|
Before you use these numbers
How the estimate works
The depth and spacing ranges come from published guide tables by soil drainage class and by texture or Ksat band (NRCS Engineering Field Handbook, Chapter 14; ASABE EP260.5; Iowa State University PM 1048; OMAFRA Publication 29). When both are known, the narrower range is shown. The depth needed at each spacing uses the Hooghoudt steady-state drain spacing equation with Moody's (1966) approximation of the equivalent depth, as printed in those guides. It is the same method Geo-Surface Pro uses for the worked spacing in its Soil information panel.
What it assumes
- One uniform soil with a single Ksat, the same in every direction, down to an impermeable layer (about 10 ft below the drain unless you enter one).
- Steady rainfall equal to the drainage coefficient, parallel laterals at equal spacing, and a free-flowing outlet that never backs up.
- A water table held at your target midway between drains, and at least 0.5 ft of head above the drain.
Why it can be wrong for your field
- The texture-class Ksat values are representative figures we chose inside the ranges USDA soil survey data commonly reports for field soils of each texture. They are not measurements of your soil. Real Ksat within one texture class commonly varies ten to a hundred times or more with structure, compaction, cracks, root channels, organic matter and layering, which is why the table also shows a slower and a faster soil.
- Structured clays often drain faster in the field than their texture suggests, and a compacted or layered soil slower. A single Ksat never describes a whole field.
- It does not consider outlet depth or capacity, grade, topography, surface water, frost, subsidence of organic soils, saline or sodic soils, envelope or filter needs, pipe hydraulics, crop needs, climate, or economics.
- It does not check drainage law, permits, wetland or environmental rules, easements, neighbouring land, or buried utilities.
What to do before any work
- Investigate the soil on site: soil survey data, test holes and, where it matters, measured conductivity.
- Follow the drainage guide for your state or province and any local rules and permits.
- Have the system designed and checked by a qualified drainage professional, and locate all buried utilities before digging.
No warranty
This calculator and its results are provided as is, for general information only, without warranty of any kind, express or implied, including accuracy, completeness or fitness for a particular purpose. You use them entirely at your own risk. To the fullest extent permitted by law, 17449275 Canada Inc., operating as GIS4AG, and its owners, employees and contractors accept no liability for any loss, damage, cost or claim of any kind arising from the use of, or reliance on, this calculator or its results. Use of this page is subject to our Terms of Service.
Design it on the real ground
In the US, Geo-Surface Pro's Soil information panel reads each map unit under your field boundary from the USDA soil survey, including the tightest layer above drain depth, and works the spacing from those measured values. Then lay out, grade and size the whole job on LiDAR. For a quick footage and cost estimate, try the tile drainage calculator.