Calculate agricultural terrace spacing from land slope, soil type, crop type, and management practice. Reduce erosion with properly spaced terraces.
Terraces are earthen ridges built across slopes to intercept runoff, reduce sheet and rill erosion, and channel water safely to outlets. Proper spacing (horizontal interval) depends on the slope steepness, soil erodibility, crop type, and management practices.
The vertical interval (VI) method is the traditional approach: VI = aS + b, where S is the land slope in percent and a and b are coefficients based on soil, crop, and practice. The horizontal interval (HI) is then derived from the VI and slope.
This calculator uses the NRCS-based vertical interval formula to determine terrace spacing for your specific field conditions, giving both the vertical and horizontal intervals for layout purposes. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process. This tool handles all the complex arithmetic so you can focus on interpreting results and making informed decisions based on accurate data.
Terraces are one of the most effective erosion control practices. Correct spacing maximizes erosion reduction without excessive loss of farmable area. This calculator replaces lookup tables with a quick, customizable estimate. Having a precise figure at your fingertips empowers better planning and more confident decisions. Manual calculations are error-prone and time-consuming; this tool delivers verified results in seconds so you can focus on strategy.
VI (ft) = (a × S) + b HI (ft) = VI / (S / 100) Where: S = field slope (%) a = slope factor (varies by soil and practice) b = base interval (varies by practice)
Result: VI = 5.0 ft; HI = 83 ft
With a = 0.6 and b = 1.4 for moderate erodibility with contour cropping: VI = 0.6 × 6 + 1.4 = 5.0 ft. HI = 5.0 / 0.06 = 83.3 ft. Terraces should be built approximately 83 ft apart horizontally.
Start at the top of the slope and work down. Use a laser level or survey transit to mark the first terrace line at the computed VI below the ridge. Each successive terrace is located one VI lower. Adjust terrace lines to follow contours and avoid sharp S-curves that complicate farming.
Every terrace must outlet to a stable conveyance: a grassed waterway, tile inlet (conservation practice called “underground outlet”), or an earthen channel. Inadequate outlets cause terrace overtopping and failure.
No-till farming reduces runoff and erosion, which may allow wider terrace spacing. Some fields with well-managed no-till and cover crops can reduce VI by 10–20%, potentially eliminating the need for one or more terrace lines on moderate slopes.
The vertical interval (VI) is the vertical height difference between successive terraces. It determines how much slope length is protected between each terrace. VI is used to calculate the horizontal spacing.
The horizontal interval (HI) is the map (horizontal) distance between terraces. It equals VI divided by the decimal slope. This is the number you measure in the field for layout.
They come from NRCS state design manuals and depend on soil erodibility (K factor), crop cover, and conservation practice. Values of a range from 0.4 to 0.8; b from 0.5 to 2.0.
Broad-base (farmable), narrow-base (grass only), steep-backslope, and bench terraces. Broad-base on gentle to moderate slopes is most common in the Midwest; steep-backslope for steeper terrain.
Yes. Annual inspection after heavy rains. Repair any breaches, low spots, or rodent damage. Maintain outlets (inlets, waterways) in good condition. Avoid tillage that moves soil into the terrace channel.
Yes. NRCS EQIP (Environmental Quality Incentives Program) typically covers 50–75% of terrace construction cost. Contact your local NRCS or Soil and Water Conservation District office.