Raised slab calculator

1. Rib wall height
   rib = height − slab
   3' 0" − 4" = 2' 8"
2. Slab
   V = L × W × slab
   43' 0" × 23' 0" × 4" = 12.21 CY
3. Rib walls
   V = rib footprint × rib height
   189.00 SF × 2' 8" = 18.67 CY
4. Concrete in all
   V = slab + rib walls
   12.21 CY + 18.67 CY = 30.88 CY
5. Insulation
   V = pocket area × rib height
   800.00 SF × 2' 8" = 2,133.33 ft³
6. Insulation pieces
   each pocket: whole pieces of the sheet size, cut to the height
   25 pockets = 25
7. Sheets to order
   full pieces: 1 sheet each; cut pieces packed onto sheets, biggest first, offcuts reused
   25 pieces = 25
8. Insulation ordered (cross-check)
   each sheet × the height it is ordered at; never less than the pockets
   25 sheets ≥ 2,133.33 ft³ = 2,133.33 ft³
9. Rib rebar
   each rib line ⌈length ÷ spacing⌉ (+1 inside; the perimeter loop shares corners)
   386' 0" of rib line ÷ 2' 0" = 204
10. Hook G (ACI 90° standard hook, out to out)
    G = 12 db + D ÷ 2 + db, D = 6 db
    6" + 1-1/2" + 1/2" = 8"
11. Each rebar (bent bar)
    ℓ = leg + G, leg = dowel + rib height + half the slab + db ÷ 2
    4" + 2' 8" + 2" + 1/4" + 8" = 3' 10-1/4"
12. Drilled hole (in)
    a carbide bit drills the middle of its ANSI B212.15 range
    5/8" bit: ( 0.650 + 0.660 ) ÷ 2 = 0.6550
13. Hole volume
    π ÷ 4 × drilled hole² × embedment
    π ÷ 4 × 5/8" ² × 4" = 1.35 in³
14. Just the gap
    hole − steel (π ÷ 4 × steel² × embedment)
    1.35 in³ − 0.79 in³ = 0.56 in³
15. Hole ⅔ full
    ⅔ × hole (the instructions say fill the hole about ⅔ full)
    ⅔ × 1.35 in³ = 0.90 in³
16. Epoxy per anchor
    (gap + ⅔ fill) ÷ 2
    ( 0.56 in³ + 0.90 in³ ) ÷ 2 = 0.73 in³
17. All anchors
    per anchor × anchors (+ tube), rounded up to a whole fl oz
    0.73 in³ × 204 = 83 fl oz
18. One cartridge gives
    cartridge less the nozzle and first-mix loss
    27.9 fl oz = 27.29 fl oz
19. Cartridges
    all anchors ÷ one cartridge, rounded up
    83 fl oz ÷ 27.29 fl oz = 4
20. Mesh sheet coverage
    c = (sheet width − lap) × (sheet length − lap)
    ( 5' 0" − 10" ) × ( 10' 0" − 10" ) = 38.19 SF
21. Mesh sheets along the length
    n = ⌈(run − lap) ÷ (sheet − lap)⌉
    ⌈( 43' 0" − 10" ) ÷ ( 10' 0" − 10" )⌉ = 5
22. Mesh sheets across the width
    n = ⌈(run − lap) ÷ (sheet − lap)⌉
    ⌈( 23' 0" − 10" ) ÷ ( 5' 0" − 10" )⌉ = 6
23. Mesh sheets
    sheets = along × across
    5 × 6 = 30
24. Without laps, for comparison
    whole sheets ⌈run ÷ sheet⌉ each way, no laps
    30 with laps − 5 added by laps = 25
25. Bar along the top of every rib (#4)
    Σ rib lines (along the slope) + laps × lap
    386' 0" + 18 × 2' 1" = 423' 6"

Where the numbers come from

• Ramp slopes (ADA): Running slope 1:12 at most (1" of rise per foot) · cross slope 1:48 at most · 30" of rise at most per run, then a level landing at least 60" long2010 ADA Standards 405.2, 405.3, 405.6 and 405.7 (U.S. Access Board guide). A walking surface steeper than 1:20 is a ramp. Existing buildings short of room may use 1:10 for 6" of rise or 1:8 for 3". The page warns past 1:12 or 30"; your local code may ask for more.Source
• Raised slab: how it is figured: Slab = L × W × thickness · rib walls and insulation pockets piece by piece × rib heightRib height = total height − slab. Pockets are the clear spaces between rib walls (default 4' × 8'); on a flat slab the odd bit at the end of a row is insulation too (into the last pocket, or a short pocket after one more rib). On a ramp (owner) full pockets are laid from the high end and what is left at the low end is solid concrete, down to 0'0" where the ramp meets grade; where the ramp is lower than the slab it is all concrete. The height changes straight along the length, so every piece uses its height averaged over it (exact for a straight slope). Rib crossings are counted once. Insulation: pieces of the sheet size in plan, tagged A, B … on the piece map, cut to the height (made to order); on a ramp each piece is a block as tall as its low end plus a wedge rising to its high end, or one tapered piece — sizes for the plant. Rib rebar: bars at a spacing, each in a hole drilled into the slab below (the dowel), up to the middle of the slab and bent there into an ACI standard 90° hook (D = 6 db, 12 db past the bend), no laps — ⌈rib line ÷ spacing⌉ per line (+1 on inside lines). Sized out to out the way rebar shops detail them (ACI 315 §3.7, CRSI): leg = dowel + rib height + half the slab + half the bar, hook G = 12 db + D ÷ 2 + db (#4: 8"), bar = leg + G. Use your drawings for rib size, spacing and dowels.
• Epoxy per anchor: Average of the gap (π ÷ 4 × (hole² − steel²) × embedment) and the hole ⅔ full (⅔ × π ÷ 4 × hole² × embedment)Installers fill the hole about ⅔ full; what the anchor pushes out of the hole is lost, so the real use is between the gap alone and the ⅔ fill — taken as the average of the two. The total is rounded up to a whole fl oz. Waste, if entered, is added on top for rough holes and hard conditions.
• Drilled hole size (ANSI B212.15): Carbide bit tips (in.): 7/16 0.458–0.468 · ½ 0.520–0.530 · 9/16 0.582–0.592 · ⅝ 0.650–0.660 · 11/16 0.713–0.723 · ¾ 0.775–0.787 · ⅞ 0.905–0.917 · 1 1.030–1.042 · 1⅛ 1.160–1.175 · 1⅜ 1.410–1.425 · 1½ 1.535–1.550A bit drills a little over its name; the hole is taken at the middle of the range (7/16 → 0.463, ⅞ → 0.911, 1½ → 1.5425). A hole size you type that is not a standard bit is used as typed.Source
• Threaded rod steel: d − 5√3 ÷ 16 × pitch: halfway between the outside of the rod and its thread root (d − 5√3 ÷ 8 × pitch) · UNC ⅜-16, ½-13, ⅝-11, ¾-10, ⅞-9, 1-8, 1¼-7Thread geometry (ASME B1.1, H = √3 ÷ 2 × pitch). The epoxy fills the thread grooves, so a rod holds less steel than a solid bar of its size (¾" → 0.6959", ½" → 0.4584"). Rebar uses its nominal size (#10 = 1.270").
• Extension tube: Past 8" deep: (embedment − 8") × 0.17 fl oz per inch, a new tube every 10 anchorsA mixing nozzle reaches about 8"; deeper holes are filled from the bottom through an extension tube, which holds 0.17 fl oz per inch (the inside of a ⅝" bore: π ÷ 4 × 0.625² = 0.307 in³ per inch) and is replaced every 10 anchors.
• Cartridges: Sizes in mL as printed, fl oz worked out (mL ÷ 29.5735) · Hilti HIT-HY 200 V3 330 / 500 mL = 11.2 / 16.9 fl oz · DeWalt AC100+ Gold 280 / 825 mL = 9.5 / 27.9 fl ozWhat a cartridge really gives, after the nozzle and the first mix: 9.07 fl oz from the 9.5 oz and 27.29 fl oz from the 28 oz AC100+ Gold. Hilti lists none, so its packs are taken at 96%.
• Hilti HIT-HY 200 V3: Bits: rod ⅜→7/16 · ½→9/16 · ⅝→¾ · ¾→⅞ · ⅞→1 · 1→1⅛ · 1¼→1⅜ · rebar #3→½ · #4→⅝ · #5→¾ · #6→⅞ · #7→1 · #8→1⅛ · #10→1½ · foil packs 330 and 500 mLHilti Anchor Fastening Technical Guide Ed. 22, Table 38 (threaded rod) and Table 18 (rebar); the same bits in grouted CMU (Masonry Anchor Design Guide 2023, Table 1); ICC-ES ESR-4868 (revised April 2026) §3.2.1 for the 330 / 500 mL packs. Hilti lists a bigger bit for deep embedment (#6 1", #7 1⅛", #8 1¼") — type it if you drill that deep. Hilti's own Volume Calculator is a phone app.Source
• DeWalt AC100+ Gold: Bits: rod ⅜→7/16 · ½→9/16 · ⅝→11/16 · ¾→⅞ · ⅞→1 · 1→1⅛ · 1¼→1⅜ · rebar #3→7/16 · #4→⅝ · #5→¾ · #6→⅞ · #7→1 · #8→1⅛ · #10→1½ · cartridges 280 mL (8478SD-PWR) and 825 mL (8490SD-PWR)DeWalt AC100+ Gold Technical Guide ©2025 rev. K (p. 2 installation, p. 29 ordering), matching ICC-ES ESR-2582 (Feb 2026) Table 9. Approved for rebar used as an anchor (embedment up to about 12 bar diameters), not for post-installed rebar development or splices.Source
• Hole size rule (the cross-check): Bit = anchor + adhesive ring, in 1/16" steps: rod + 1/16" up to ⅝", + ⅛" above · rebar (actual size) + ⅛" · every maker's bit is checked to leave 1/32"–3/16" of ring each sideA cross-check on every maker's bit, and the answer wherever a maker's number cannot be found. Makers may call for a different size — type your hole size if so.
• Method source: DeWalt Adhesive Anchor Volume EstimatorThe ⅔ fill, the extension tube and the usable cartridge follow it; every number on this page is also worked out by math.Source
• Rebar weights (ASTM A615): #3 0.376 · #4 0.668 · #5 1.043 · #6 1.502 · #7 2.044 · #8 2.670 · #9 3.400 · #10 4.303 · #11 5.313 lb/ftASTM A615 Table 1 nominal weights, as listed on Harris Supply Solutions' "Concrete Reinforcing Bar Products" sheet. Each equals the bar area × 3.40 lb/ft per in² (steel at about 490 lb/ft³): #4 = π × 0.5² ÷ 4 = 0.1963 in² × 3.40 = 0.668 lb/ft.Source
• Welded wire mesh lap: 10 in by default (ACI minimum: one mesh square + 2 in = 8 in for 6×6 mesh) · sheets 5' × 10'ACI 318-19 §25.5.4 (plain welded wire in structural slabs) and ACI 439.5R-18 §6.4 both give one square plus 2 in, as summarized by ASCC (Jan 2021); 10 in is more than that minimum. 6×6-W1.4×W1.4 is the usual minimum temperature mesh on composite deck (SDI). Your engineer may call for a different lap — type it in. Sheets are counted laid the way that takes fewer, with no offcuts reused; counted by area, offcuts are assumed reused, so order extra.Source
• Bar along the top of the ribs (with wire mesh): One continuous #4 along every rib, in the slab: the perimeter loop and every inside rib lineCommon practice when the slab on the ribs is reinforced with wire mesh. Counted on the rib centre lines (lines along a ramp follow the slope), lapped where a line is longer than a stock bar with the ACI Class B lap at 4,000 psi (25" for #4). Corners of the perimeter loop are not lapped extra. Use your drawings.
• Lap splice (ACI 318-19 Class B): 4,000 psi, Grade 60, uncoated: #3 19" · #4 25" · #5 31" · #6 37" · #7 54" · #8 62" · #9 70" · #10 79" · #11 87"Class B tension lap = 1.3 × ℓd (§25.5.2.1), ℓd from Table 25.4.2.3: fy ÷ (25 λ √f'c) × db for #6 and smaller, ÷ 20 for #7 and larger, rounded up, at least 12". Assumes bars not cast with more than 12" of concrete below them, uncoated, cover ≥ db and spacing ≥ 3 db — usual for a slab grid. Lightweight concrete: λ = 0.75 (longer lap). Same as Table 1.11 of the Dayton Superior Rebar Splicing Handbook (Other bars, Case 1, Class B) at 3,000 and 4,000 psi; at 5,000 psi #4, #6, #8 and #10 come out 1" longer here because they are rounded up. Use the lap on your structural drawings when it is given.Source