Ontario · Quantities · 2026
How much sand and stone does a septic bed take? The real formulas
Stone is bought by the cubic metre and delivered by the truckload — and a truck that arrives short with an open excavation is the most expensive kind of mistake. Here are the quantities, the waste factors, and a full worked example.
The two rules of ordering: quantities come from the EXCAVATION footprint (bed + 1 ft over-dig each side), and everything gets a waste factor — 10% on stone and sand. Textbook math without those two corrections runs 10–15% short.
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The part nobody tells you
Designers charge $800–$2,000 just for the paperwork in these quotes.
Ontario law lets you do that part yourself, on your own property. OntarioSepticDesigner.ca turns your answers into the same 26-page package the township clerk sees every day — calculations, drawings, forms, all of it.
Stone: the formula
A conventional trench bed carries washed septic stone around each distribution pipe — below, beside, and above it. Per Code minimums, the working volume is:
Stone volume
runs × run length × 0.6 m (trench width) × 0.25 m (stone depth) × 1.10 waste
For our worked example — 3-bedroom house, Q = 1,600 L/day, T = 18, which needs 144 m of pipe in 5 runs of 28.8 m: 5 × 28.8 × 0.6 × 0.25 = 21.6 m³, order 23.8 m³. At 1.5 tonnes per cubic metre that is roughly 36 tonnes — two tandem loads and change.
Sand: only if the bed comes up
A conventional in-ground bed in decent soil needs no imported sand. Sand enters when your water table, bedrock, or slow soil forces a raised or partially raised bed — then it becomes the biggest single material line on the job:
Sand volume (raised bed)
fill area × average fill depth × 1.10 waste — and the fill area is much bigger than the bed, because raised fill needs shallow side slopes (roughly 4:1) running down to grade on every side.
A modest fully raised bed — 20 m × 15 m fill pad averaging 0.9 m deep — is 270 m³ plus waste: almost 300 m³ of specified filter sand, around 450 tonnes, 20+ truckloads. That is why raised beds cost $10,000–$20,000 more and why trucking distance matters so much on rural lots.
Not any sand, not any stone
The Code specifies both. Filter sand must meet the percolation spec (roughly T of 6–10 when tested) — pit-run or masonry sand fails and the inspector can make you remove it. Stone must be clean, washed, in the Table 8.7.3.4 sizes; dirty gravel full of fines plugs a new bed years early. Order “septic stone” and “filter sand to OBC spec” by name and keep the supplier tickets for your inspection file.
The $18,950 line that never appears on a quote
A real worked example: 3-bedroom bungalow, conventional bed. Tank supplied and set, pipe, stone, fabric, one day of machine and labour, permit allowance — $13,049 with HST. The same job quoted at $32,000. The gap is design fees, markup, and labour you may not need to buy.
Two minutes on the free checker shows the numbers your own lot generates — daily flow, tank size, risk level — before anyone quotes you.
The rest of the takeoff
Stone and sand travel with three companions on the order sheet: filter fabric to cover the stone (bed area plus overlap), the pipe itself (design length × 1.20, in 10 ft sticks), and backfill — usually the native material from the over-dig, which is why the full material list prices machine time from the excavation footprint, not the drawing. Every quantity on that list comes from the same three inputs: your bedroom count, your T-time, and your water depth.
Quantity questions, answered straight
How many tonnes of stone for a septic bed?
Volume × about 1.5 t/m³. A typical 3-bedroom conventional bed runs 22–24 m³ ordered — roughly 33–36 tonnes.
How much sand for a raised septic bed?
Fill area × average depth × 1.10. Because of the 4:1 side slopes the pad dwarfs the bed itself — fully raised beds commonly need 200–300 m³ of spec filter sand.
Can I use pit-run sand?
No. Raised-bed fill must be filter sand meeting the OBC percolation spec. Wrong sand is a tear-out order, not a warning.
What size is septic stone?
Clean washed stone in the Table 8.7.3.4 range — order it as “septic stone” and your yard will know exactly what you mean.
Your takeoff, calculated from your lot
The builder turns your bedroom count, T-time and water depth into the full material order — stone, sand, pipe, fabric, with waste factors applied. Part of the $99.99 package.