Retaining Wall Calculator — ft, blocks, cost
How to use this calculator
Select wall type (landscape blocks, poured concrete, or timber/railroad ties), enter wall length and height in feet and inches, then configure materials and drainage. The calculator returns course count, material quantities, gravel backfill tonnage, drain pipe, filter fabric, geogrid, and an itemized cost estimate.
Blocks — choose standard (12×4×8″) or large (18×6×12″) landscape blocks with setback per course.
Concrete — tapered gravity wall with top/base thickness and optional rebar.
Timber — 6×6 or 6×8 railroad ties with deadman anchors.
Drainage — gravel backfill, drain pipe, filter fabric, and geogrid for walls over 4 ft.
Saved Calculations
| Time | Type | L×H | Material | Gravel | Cost |
|---|
How to Calculate Materials for a Retaining Wall
Segmental retaining wall (SRW) coursing follows TMS 402/602 and NCMA SRW design. Course count is wall height ÷ block height, rounded up; blocks per course is wall length ÷ block length, rounded up. The result is multiplied by the waste factor (5% for blocks, 10% for cut-heavy concrete and timber). For a long straight run this calculator over-estimates slightly because corner and end-cap units are billed as full blocks — order the nearest pallet quantity.
Block, concrete and timber walls
Standard blocks (12×4×8″, ~30 lbs) suit gravity walls up to 4 ft; large blocks (18×6×12″, ~65 lbs) for taller runs. A ¾″ setback per course gives roughly 5–7° batter for sliding/overturning resistance. For mortared CMU or grouted-cell stem walls instead of dry-stacked units, size the units with the block wall calculator and the mortar and grout with the mortar & grout calculator. Poured-concrete gravity stems are taken as a tapered section (average of top and base thickness); detail and bar the section with the concrete beam & rebar calculator and price ready-mix or bagged mix with the concrete bag calculator.
Drainage and reinforcement
A 12″ wide clean-stone chimney drain behind the wall, a 4″ perforated pipe daylighted at the base, and a filter-fabric envelope relieve hydrostatic and frost pressure — the leading cause of SRW failure. Gravel is taken at 100 lb/ft³ (≈1.35 tons/yd³). Geogrid is recommended on walls over 4 ft (1.2 m); embedment length is the larger of 60% of wall height or 4 ft. A clean stone face can also be dressed with the stone veneer calculator.
Formulas
Courses = ⌈H ÷ block height⌉ · Blocks = ⌈L ÷ block length⌉ × courses × (1 + waste). Concrete volume (yd³) = L × H × ((t_top + t_base) ÷ 2) ÷ 27 × (1 + waste). Gravel (tons) = L × H × depth × 100 ÷ 2000. Geogrid rolls = ⌈layers × L × embedment ÷ 50⌉.
On install day
Three things estimators forget on SRWs. Bury the first course — NCMA SRW design guide calls for 1 in of embedment per 8 in of exposed wall (a 4 ft wall buries roughly 6 in plus 6 in of leveling-pad gravel), so order an extra row of blocks and don't count the buried course as "exposed face" on your $/ft² quote. Cap blocks and corners — caps are sold separately at $5–9 each in 2025 USA (vs. $3.50–5 for face blocks) and 90° corner units run 20–30% more; for any wall over ~30 ft, add 2–3 caps for cut waste at returns. Pallet quantities — landscape blocks ship 60–112 per pallet at $350–900/pallet delivered; ordering 105% of net almost always rounds you up to the next pallet, so buy by the pallet and use leftovers for the next phase. Walls over 4 ft (1.2 m) tall or carrying a driveway / pool surcharge need a stamped IRC §R404 design with geogrid — this calculator's geogrid quantity is a takeoff aid, not a substitute for the engineer's layout.
FAQ
How tall can I build without engineering? Most jurisdictions allow gravity walls up to 4 ft (measured bottom of footing to top) without a stamped design. Taller walls, tiered walls, or walls with a surcharge typically require engineering drawings and geogrid reinforcement.
How much gravel do I need behind a retaining wall? Standard practice is a 12″ clean crushed-stone zone behind the wall over the full height. This calculator converts that volume to tons at 100 lb/ft³.
