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Terrace Spacing Calculator — Bench Terrace Vertical Interval

Find the right vertical spacing between bench terraces on a slope — how far apart to step them so each bench is level, given how steep the land is, how wide you want each bench, and how the riser between benches is built.

Vertical interval (spacing)0.71 m
Horizontal width per terrace2.35 m

How to measure your inputs

  • Land slope: rise over run × 100 — a level or clinometer app on a phone works well over a measured distance.
  • Bench width: how wide you want the flat, usable part of each terrace step.
  • Riser type: a steeper riser (lower ratio) needs more stable soil or a real retaining structure; a gentler riser is safer on loose ground but uses more horizontal space per terrace.

Methodology

Bench-terrace geometry: VI = (S × Wb) ÷ (100 − S × U), where S is slope percent, Wb is bench width, and U is the riser's horizontal-to-vertical ratio. This comes from requiring the natural ground's drop across one bench-plus-riser span to equal the vertical interval itself — a deterministic geometric relationship, not an empirical regional formula, so it holds regardless of soil type or climate (soil type instead determines which riser option is actually safe to build).

How bench terrace spacing actually works

Vertical interval vs. terrace height

The vertical interval (VI) is the height of one riser — the drop from one bench's level to the next. It's not the same as the total height of the slope you're terracing; divide your slope's total height by the VI to get how many terraces you actually need, which this calculator does automatically when you fill in the optional height field.

Choosing a riser type actually matters for safety

A steep riser (low horizontal:vertical ratio, like 0.2:1 stone facing) packs more vertical drop into less horizontal space, which sounds efficient — but only holds up if the material can resist slumping. On loose or sandy soil, a gentler riser (0.5:1 to 1:1, compacted earth or vegetated) is the safer default even though it uses more land per terrace; this is exactly why the calculator asks for riser type rather than assuming one fixed ratio.

When terracing stops being the right answer

As slope percent climbs, the denominator in the vertical-interval formula (100 − S×U) shrinks, and vertical interval grows fast — meaning fewer, taller, riskier risers per terrace. Past roughly 40-50% slope with anything other than a stone-faced or engineered riser, terracing usually needs professional structural input rather than a DIY build; that's the point where a site-specific consultation is worth more than another calculator run.

Frequently asked questions

What's the difference between vertical interval and terrace height?

Vertical interval is the height of a single riser between two benches. Terrace height (or total slope height) is the full vertical distance being terraced — divide it by the vertical interval to get how many terraces you need.

How wide should a terrace bench be?

Wide enough for what you'll actually do on it — a walking path or narrow planting bed can be under 1m, while a bench meant for vehicle access or wide crop rows often needs 2-4m. Wider benches also mean a larger vertical interval for the same slope, so there's a real trade-off between usable width and how many terraces you end up building.

Do terraces work on any slope?

Terracing suits roughly 5-40% slopes well with standard riser types. Below about 5% the benefit over just gently grading the land is minimal; above about 40-50%, riser height grows quickly and stability becomes a real engineering concern rather than a DIY decision.

What if my slope is too steep for a DIY terrace?

Get a site-specific structural assessment before building — steep terracing that fails can slump or slide, which is far more costly than the original erosion problem it was meant to solve. Swales' Professional Services offers on-site swale and earthworks design for exactly this kind of case.