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Fir mulch chart
Put your fir mulch area, depth and waste in: 900 square feet at 4 inches with 10% waste needs 990.00 square feet — 12.22 cubic yards exact, order 13 cubic yards.
★ CONSTRUCTION · REFERENCE TABLE #492 · FIR MULCH
Fir Mulch Chart: 900 Sq Ft at 4 Inches, Order 13 Yards
On the defaults — 900 square feet at a 4-inch depth with 10% waste — fir mulch needs 990.00 square feet of coverage, which is 12.22 cubic yards exact, so order 13 cubic yards. This is reference table #492 — the fir version of the mulch chart, with a calculator on top and a 16-row lookup table below, following the sycamore-mulch-chart page, the beech-mulch-chart page, and the juniper-mulch-chart page — the same 324-square-foot rule, fir beds.
What does 12.22 cubic yards of fir mulch mean?
It means 990.00 square feet of bed, once 10% waste is added to 900 square feet, covered 4 inches deep. A cubic yard covers 324 square feet at 1 inch, so at 4 inches one yard covers only 81.0 square feet, and 990.00 ÷ 81.0 is 12.22 yards. The order rounds up to 13 because mulch is delivered by the whole yard: ordering 12 would leave about a fifth of a yard short, and a thin patch at the far end of the last bed. The 0.78-yard gap between exact and order is the safety margin the rounding buys you, not waste.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Needed area | area × (1 + waste ÷ 100) | 990.00 sq ft — 900 × 1.10. |
| Exact cubic yards | needed area × depth ÷ 324 | 12.22 — 990.00 × 4 ÷ 324. |
| Order | exact cubic yards rounded up | 13 cubic yards — 12.22 rounded up. |
| Coverage per yard | 324 ÷ depth | 81.0 sq ft per yard — 324 ÷ 4. |
| Area behind a target exact figure | target exact × 324 ÷ depth ÷ (1 + waste ÷ 100) | 900 sq ft — 12.22 × 324 ÷ 4 ÷ 1.10. |
| Depth behind a target exact figure | target exact × 324 ÷ needed area | 4 inches — 12.22 × 324 ÷ 990.00. |
| Waste behind a target exact figure | (target exact × 324 ÷ depth ÷ area − 1) × 100 | 10% — (12.22 × 324 ÷ 4 ÷ 900 − 1) × 100. |
Three things to check before you trust the number
First, the area must be beds only: lawn, paths and patios inside your outline are not mulched, and counting them inflates the order by their full share. Second, the depth must be the finished depth after settling, not the depth straight off the truck — fir mulch settles, so a bed that measures 4 inches on delivery day may sit at 3 inches within weeks. Third, the waste figure must match the ground: 10% suits flat, easy beds, but a steep slope, many small beds, or a long wheelbarrow run can eat 15% before the last bed is covered.
Worked example
Area 900 square feet, depth 4 inches, waste 10%. Needed area: 900 × 1.10 = 990.00 square feet. Exact cubic yards: 990.00 × 4 ÷ 324 = 12.22. Order: 13 cubic yards. Change only the depth to 3 inches and the exact figure falls to 9.17, order 10; change only the area to 1000 square feet and it rises to 13.58, order 14. Depth moves the answer in proportion, area moves it in proportion, and waste moves it by its own percentage — no step in the chain hides another.
Fir mulch lookup table
Every row below is the same formula at 10% waste: needed area is area × 1.10, exact cubic yards are needed area × depth ÷ 324, and the order is the exact figure rounded up. Rows vary in both area and depth, so a shallow small bed and a deep large one can both be read off directly. Find your row, or use the calculator above for any size the table does not list.
| Area (sq ft) | Depth (inches) | Needed area (sq ft) | Exact cubic yards | Order |
|---|---|---|---|---|
| 350 | 2 | 385.00 | 2.38 | 3 cubic yards |
| 550 | 3 | 605.00 | 5.60 | 6 cubic yards |
| 800 | 2 | 880.00 | 5.43 | 6 cubic yards |
| 450 | 4 | 495.00 | 6.11 | 7 cubic yards |
| 1000 | 3 | 1,100.00 | 10.19 | 11 cubic yards |
| 650 | 4 | 715.00 | 8.83 | 9 cubic yards |
| 1200 | 2 | 1,320.00 | 8.15 | 9 cubic yards |
| 900 | 4 | 990.00 | 12.22 | 13 cubic yards |
| 1500 | 3 | 1,650.00 | 15.28 | 16 cubic yards |
| 2000 | 3 | 2,200.00 | 20.37 | 21 cubic yards |
| 600 | 4 | 660.00 | 8.15 | 9 cubic yards |
| 1100 | 4 | 1,210.00 | 14.94 | 15 cubic yards |
| 1400 | 2 | 1,540.00 | 9.51 | 10 cubic yards |
| 1800 | 4 | 1,980.00 | 24.44 | 25 cubic yards |
| 250 | 3 | 275.00 | 2.55 | 3 cubic yards |
| 3000 | 4 | 3,300.00 | 40.74 | 41 cubic yards |
Every branch, checked
900 square feet at 4 inches with 0% waste gives 11.11 cubic yards exact, order 12. The same area at 3 inches with 10% waste gives 9.17 cubic yards exact, order 10. A 1000-square-foot area at 4 inches with 10% waste gives 13.58 cubic yards exact, order 14. An 800-square-foot area at 4 inches with 10% waste gives 10.86 cubic yards exact, order 11. Each branch changes exactly one input, so the difference from 12.22 isolates that input.
The reverses, worked backwards
The area behind 12.22 cubic yards is 900 square feet: at 800 the figures are 10.86 cubic yards exact, order 11, and at 1000 they are 13.58 cubic yards exact, order 14 — a 100-square-foot step moves the exact figure by about 1.36 yards at this depth. The depth behind 12.22 cubic yards is 4 inches: at 3 inches the figures are 9.17 cubic yards exact, order 10, and at 5 inches they are 15.28 cubic yards exact, order 16 — one inch at this size is worth just over 3 yards. The waste behind 12.22 cubic yards is 10%: at 5% the figures are 11.67 cubic yards exact, order 12, and at 15% they are 12.78 cubic yards exact, order 13 — five points of waste move the order by about half a yard here, and only the rounding decides whether the order itself changes.
What the defaults assume
The defaults assume a flat 900 square feet of bed, a uniform 4-inch finished depth, and 10% waste for settling, spillage and uneven ground. Real beds vary: a bed that is 4 inches in the middle and 2 at the edges needs its average depth, not its deepest point, and a sloped bed needs more waste than a flat one. Zero square feet is the honest edge: 0.00 cubic yards exact, order 0. Negative area, zero depth and negative waste are rejected — none of them describes a real bed.
Who uses this
A homeowner mulching the beds before a delivery: the area is the beds measured once, the depth is the finished layer wanted, and the order is the number to give the yard. A landscaper quoting a job: the same three inputs price the mulch line, and the lookup table answers a client’s “what if it were deeper” without a second calculation. A garden-center customer ordering delivery: the exact figure says what the beds need and the rounded order says what the truck brings. An allotment holder splitting a load: the table shows each plot’s share, so a 13-yard order divides fairly between neighbours.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is in the inputs. An area that counts paths, a depth measured before settling, or a waste figure guessed for the wrong ground will each move the answer by exactly the amount of the error, every yard. The model assumes a uniform depth and a rectangular-area measure — irregular beds should be split into rectangles and added, and sloped beds measured along the slope, not the flat map. Fir mulch settles and breaks down over the season, so re-measure depth before topping up. This page is a calculation tool, not landscaping advice.
Cite this calculator
Fir mulch 900 sq ft at 4-inch depth with 10% waste needs 990.00 sq ft — 12.22 cubic yards exact, order 13. Free calculator plus 16-row lookup table. Source: Bright Side Kit, https://brightoolbox.com/fir-mulch-chart/, accessed 30 October 2026 (2026-10-30).
Frequently asked questions
Where does the 324 come from?
One cubic yard is 27 cubic feet, and one inch of depth over one square foot is 1/12 of a cubic foot — so a yard covers 27 ÷ (1/12) = 324 square feet at 1 inch. Divide 324 by your depth in inches and you get the coverage per yard at that depth: 81.0 square feet at 4 inches.
Why round the order up instead of to the nearest yard?
Because a short delivery leaves a bed unfinished, while a small surplus tops up thin spots and settles in. At 12.22 exact, ordering 12 would leave about a fifth of a yard short; ordering 13 covers the beds with 0.78 yards to spare.
How much waste should I allow?
10% suits flat, easy beds. Use 5% only for a single flat rectangle with a short carry, and 15% for slopes, many small beds, or a long wheelbarrow run. When in doubt, take the higher figure — the cost of a spare half-yard is far below the cost of a second delivery.
Does fir mulch need a different depth than other mulches?
No — the chart’s math is the same for any mulch, because it only converts area and depth into volume. What differs is how a mulch behaves: fir breaks down over the season, so a 4-inch layer laid now will sit thinner by autumn, and that is a reason to re-measure before topping up, not a reason to change the formula.
How do I measure an irregular bed?
Split it into rectangles and triangles, measure each piece, and add the areas. A curved bed measured as one big rectangle overstates the area by the corners you do not mulch; splitting it keeps the order honest.
What if my beds are on a slope?
Measure the area along the slope, not the flat map distance, and allow 15% waste: mulch migrates downhill in rain, and the top of a slope thins first. Enter the slope-measured area and the higher waste, and the order will cover the whole bed.