Your Result Explained: Exact Takeoff Breakdown
A 10 ft by 12 ft ground-level floating patio deck (120 square feet) is one of the easiest weekend DIY backyard projects because a low freestanding platform (typically under 30 inches above grade and not attached to the house ledger) often rests on precast concrete deck blocks over compacted gravel Pads rather than requiring deep frost-line ledger engineering.
By choosing 12-foot stock 5/4×6 deck boards (5.5 inches actual width) to span the full 12-foot length continuously with a 1/8-inch (0.125") gap, each row covers 5.625 inches (0.46875 ft). Covering the 10-foot (120-inch) width requires 21.33 net rows (256.00 net linear feet). Because 12-foot boards match the 12-foot deck length with almost zero end cut-off waste, a conservative 5% waste factor brings your total to 268.8 linear feet—or 23 twelve-foot deck boards. Framing the 12-foot length at 16 inches on-center requires 10 ten-foot interior/end joists (9 bays + 1 starter) plus 2 twelve-foot outer rim joists for 12 total framing boards. Fastening takes 404 deck screws (2 boxes of 350), and spreading a 3-inch #57 crushed stone drainage pad underneath takes 31.50 cubic feet (1.17 cubic yards / 1.58 tons, or 63 fifty-pound bags).
On a low floating deck with only 6 to 8 inches of ground clearance, the 1.17 cubic yards of #57 crushed stone underneath is critical—it supports your concrete deck blocks without settling into soft mud and prevents ground moisture from rotting the low joists.
Step-by-Step Math for a 12 ft × 10 ft Floating Deck (120 Sq Ft)
Computing 12-foot 5/4×6 deck boards, 16" OC joists, screws, and 3-inch under-deck gravel base for a 12 ft × 10 ft floating deck with 5% waste.
- Net deck area: 12 ft × 10 ft = 120 sq ft (11.15 sq m).
- Effective row coverage width: (5.5" board + 0.125" gap) ÷ 12 = 0.46875 ft.
- Net linear feet of decking: 120 sq ft ÷ 0.46875 ft = 256.00 linear ft (21.33 rows of 12 ft).
- Adjusted linear feet (+5% waste): 256.00 × 1.05 = 268.80 linear ft.
- 12-ft deck board count: ⌈268.80 ÷ 12 ft⌉ = 23 twelve-foot boards.
- Framing joists (16" OC along 12 ft length): ⌈(12 × 12) ÷ 16⌉ + 1 + 2 rim boards = 12 joists.
- Deck screws (2 per crossing): ⌈268.80 × (12 ÷ 16) × 2⌉ = 404 screws (2 boxes of 350).
- 3-inch under-deck #57 gravel: (120 × (3 ÷ 12) × 1.05) ÷ 27 = 1.17 cubic yards (63 bags at 0.5 cu ft).
Bottom Line: Order 23 twelve-foot 5/4×6 deck boards (268.8 linear ft), 12 framing joists/rims, 404 exterior deck screws, and 1.17 cubic yards of #57 gravel.
How This Scenario Is Calculated
We multiply 12 ft by 10 ft to get 120 sq ft, divide by 0.46875 ft effective row width (5.5" board + 0.125" gap) to get 256.00 net linear feet, and multiply by 1.05 for 5% waste to reach 268.8 linear feet—which divides by 12 feet per board to equal 23 twelve-foot deck boards.
Dividing the 144-inch (12 ft) length by 16" on-center spacing yields 9 bays (10 ten-foot joists) plus 2 twelve-foot outer rim joists = 12 framing boards. Multiplying 268.80 linear feet by 1.5 screws per foot equals 404 screws, and 120 sq ft at 3 inches deep (+5% waste) equals 31.50 cubic feet (1.17 cubic yards) of #57 stone.
Row Width (ft) = (Board Width In + Gap In) ÷ 12 | Linear Ft = (Area ÷ Row Width) × (1 + Waste%) Deck Boards = ⌈Linear Ft ÷ Board Length Ft⌉ | Joists = ⌈(Span Ft × 12) ÷ Joist Spacing In⌉ + 3 Screws = ⌈Linear Ft × (12 ÷ Joist Spacing In) × 2 Screws/Crossing⌉ Project-Specific Tips & Common Mistakes
Select "Ground Contact" (UC4A) Rated Pressure-Treated Joists
Because a floating patio deck sits within 6 to 12 inches of the ground where humidity stays high, standard "Above Ground" (UC3B) treated 2×6s can rot prematurely. Always check the end tags on your 12 framing joists for "Ground Contact AWPA UC4A" treatment.
Compact Crushed Stone Footing Pads Under Every Concrete Deck Block
Never place precast concrete deck pier blocks directly on grass or soft topsoil. Excavate sod across the 10×12 footprint, lay woven geotextile fabric, and tamp your 1.17 cubic yards of #57 crushed stone flat so none of the deck blocks sink after heavy rain.
Leave a 1-Inch Air Gap Around the Bottom Perimeter for Ventilation
If you wrap the outer rim joists with fascia or skirting boards, leave at least a 3/4-inch to 1-inch clearance gap above the gravel so cross-breezes can dry out the underside of the 10×12 frame.
Mistake Attaching a floating deck on surface blocks to the house wall
Recommended Fix: A deck resting on surface pier blocks moves slightly with seasonal frost and soil moisture. Never bolt a floating deck to a house foundation or ledger—keep it 1 to 2 inches freestanding from the siding.
Mistake Using 2×4s instead of 2×6s for floating deck floor joists
Recommended Fix: Even on a ground-level deck, 2×4 joists bounce noticeably between pier blocks and hold less screw thread depth. Frame your 10×12 box with Ground-Contact 2×6s or 2×8s supported every 5 to 6 feet by concrete deck blocks.
Reference Coverage Table (#57 Crushed Stone (3/4" Clean Angular Limestone/Granite))
Compare how coverage changes across common depths for #57 Crushed Stone (3/4" Clean Angular Limestone/Granite) (default planning density 2700 lbs/yd³):
| Depth | 1 Cubic Yard Covers | 1 Ton Covers | Yards / 100 sq ft | Tons / 100 sq ft | Bags (0.5 ft³) / 100 sq ft |
|---|---|---|---|---|---|
| 2 in | 162 sq ft | 120 sq ft | 0.62 yd³ | 0.84 tons | 34 bags |
| 3 in Active | 108 sq ft | 80 sq ft | 0.93 yd³ | 1.26 tons | 50 bags |
| 4 in | 81 sq ft | 60 sq ft | 1.23 yd³ | 1.66 tons | 67 bags |
Reference Source: FHWA Aggregates Reference & ASTM C29 bulk density standard (95–105 lbs/ft³).
Frequently Asked Questions
How many 12-foot deck boards do I need for a 10×12 deck?
Running 12-foot boards along the 12-foot dimension across a 10-foot (120-inch) width requires 22 net boards (21.33 rows), or 23 boards when including a 5% waste buffer (24 boards with 10% waste).
How many concrete deck blocks do I need for a 10×12 floating deck?
When framing a 10×12 floating deck with 2×6 joists, use 9 or 12 precast concrete deck blocks arranged in 3 rows of 3 (spaced 5 ft × 6 ft) or 3 rows of 4 (spaced 5 ft × 4 ft) so no 2×6 span exceeds 5 to 6 feet.
How many joists are in a 10×12 floating deck at 16" OC?
Spacing joists 16 inches on-center along the 12-foot length requires 10 ten-foot joists (including the two 10-foot ends) plus 2 twelve-foot outer rim boards—totaling 12 framing boards.
How much gravel do I need under a 10×12 floating deck?
A 3-inch layer of #57 crushed stone over 120 sq ft (with 5% waste) requires 31.50 cubic feet, which is 1.17 cubic yards (1.58 tons) in bulk or 63 fifty-pound bags.
Do I need a building permit for a 10×12 floating deck?
Under the International Residential Code (IRC R105.2), freestanding decks that are under 200 square feet, less than 30 inches above grade at all points, not attached to the dwelling, and not serving the required exit door are exempt from permits in many municipalities—always verify with your local building department and HOA.