CMU block calculator

1. Wall area
   A = length × height
   20' 0" × 8' 0" = 160.00 SF
2. Blocks per SF
   144 ÷ (16" × face height), nominal sizes include the joint
   144 ÷ (16 × 8) = 1.000
3. Blocks
   net area × per SF, rounded up
   160.00 SF × 1.000 = 160
4. Mortar (80 lb preblended bags)
   standard units ÷ 16 per bag
   160.00 SF × 1.125 ÷ 16 = 12
5. Grout in the rebar cells (mold-book void)
   bar locations × (height ÷ 8") courses × void per cell
   7 × 8' 0" ÷ 8" × 258.2 in³ = 12.55 ft³
6. Block weight (normal weight, 137 lb/ft³)
   blocks × unit weight (mold book)
   160 × 40.02 lb = 6,403 lb
7. Grout
   cells: wall SF × TEK 4-2A Table 3 ft³ per 100 SF (by width and spacing) ÷ 100; bond beams: LF ÷ LF per bag × 0.66 ft³
   160.00 SF = 12.55 ft³
8. Vertical bars at the spacing
   wall length ÷ spacing, rounded up, + 1 (a bar at each end)
   20 × 12 ÷ 45 (in), rounded up, + 1 = 7
9. Lap length
   bar diameter × lap diameters
   #5: 0.625 × 48 (in) = 2' 6"
10. Vertical steel
    bars × wall height
    7 × (8) (ft) = 56' 0"
11. #5 weight
    feet × lb per foot (ASTM A615)
    56 × 1.043 = 58.4 lb
12. #5 stock bars
    full pieces + cut pieces packed into stock bars
    20' bars = 4
13. Joint reinforcement rows
    height ÷ spacing, rounded up, − 1 (none in the top joint)
    8' 0" ÷ 1' 4" = 5
14. Joint reinforcement, length
    rows × wall length
    5 × 20' 0" = 100' 0"
15. Joint reinforcement, pieces
    per row ⌈(length − piece) ÷ (piece − lap)⌉ + 1, × rows
    3 × 5 = 15

Where the numbers come from

• Blocks per square foot: 144 ÷ (length × height): 8" × 18" = 1.000 per SF, 8" × 16" = 1.125 per SFWorked out from the nominal face, which already includes the ⅜" joint (actual 7⅝" × 17⅝" or 7⅝" × 15⅝"). CMHA/NCMA TEK 4-2A gives 119 per 100 SF of 8" × 16" including about 5% waste: 112.5 × 1.05 = 118.1, which agrees. 8" × 18" block is the page default; it has two cells 9" apart, so grout and bars land on a 9" grid.Source
• Mortar: One 80 lb bag of preblended mortar lays about 16 standard block (face-shell bedding)TEK 4-2A Table 2, a rule of thumb that already includes nominal waste. Masonry cement: 8 × 70 lb bags + 1 ton sand ≈ 240 block. Mortar use varies with the mason and the layout.Source
• Block void and weight: From the supplier's mold book (Besser unit calculations): 8" × 18" hollow 504.75 in³ net, 40.02 lb normal / 29.21 lb lightweight; 75% solid 793.83 in³, 62.94 / 45.94 lbSuperior Block Corp (Brooklyn) mold book, Besser drawings: each unit's net concrete volume and weight at 100 lb/ft³ (lightweight) and 137 lb/ft³ (normal weight). Grout fills the void = W × H × L − net (the cores plus the end flanges), half of it per cell; a column of cells is the wall height ÷ 8" courses. 8" × 18" hollow (02-724817): 1,021.1 − 504.75 = 516.4 in³, 258.2 per cell. 6" 02-211431, 8" × 16" 02-726809, 10" 517602, 12" 517606; 75% solid 517599, 474106, 517604, 517608. TEK 4-2A Table 3 prints more grout per SF than these voids (e.g. 8" × 16" every cell 36.1 ft³ per 100 SF with 3% waste vs 26.9 from the void) — grout also fills the joints and spills; add waste. Sizes not in the book use TEK.
• Wall given by area: Rebar and joint reinforcement assume a 12' high wall: length = area ÷ 12'Bars and joint reinforcement depend on the wall's length and height, not just its area. With only the area, the page takes a 12' high wall (the length is the area ÷ 12') for a first, minimal count — enter the length and height for the real wall.
• Joint reinforcement: A row in the bed joint every 16" up the wall (none in the top joint), 10' pieces lapped 6"NCMA TEK 12-02B: "typical joint reinforcement spacing is 16 in. on center"; splices "a minimum of 6 in."; W1.7 (9 gage) is the most common wire. 10' standard pieces: Hohmann & Barnard (https://h-b.com/products/continuous-wire). Rows = ⌈height ÷ spacing⌉ − 1; length = rows × wall length (openings not taken off — a little extra); pieces per row = ⌈(length − piece) ÷ (piece − lap)⌉ + 1. Order the width for your block. Corners and tees: prefabricated pieces, count them from your drawings.Source
• Grout: TEK 4-2A Table 3, ft³ per 100 SF — every cell: 6" 25.6 · 8" 36.1 · 10" 47.0 · 12" 58.9; at 48": 4.3 · 6.1 · 7.9 · 9.9 (rows for 16, 24, 32 and 40" too)TEK 4-2A Table 3 (two-core block, 3% waste), the row for your width and spacing. TEK Table 4 counts cores per bag and gives more bags than volume ÷ 0.66; the app uses Table 3 volume. Bond beams: Table 5, 80 lb bag of preblended grout ≈ 0.66 ft³ fills 2.7 LF of 6", 2.0 LF of 8", 1.6 LF of 12" bond beam. Grouting 4" block is not recommended.Source
• Bar layout: Vertical: ⌈wall length ÷ spacing⌉ + 1 (a bar at each end) + 2 per opening; bond beams: bars × wall lengthGeometry only. Real bars sit in the block cells, so the spacing is a multiple of 8" and a bar can move a cell to clear an opening or a control joint. Bars at corners, wall intersections and jambs follow your structural drawings.
• Lift bars (6'8"): Low-lift grouting: build at most 5'4", set the bars, grout, repeat — bars are spliced at each pour heightCMHA CMU-FAQ-005: low-lift sections are no taller than 5'4" and "continuity of the reinforcement is maintained by splicing between each section". 6'8" (80") is a 20' bar cut in three with no waste, short enough for the mason to lift block over. In a 4' (48") lift it sticks up 80 − 48 = 32" — a full lap for #4 (24") and #5 (30") at 48 diameters, but not #6 (36"). A new bar is set at every pour height, so pieces per location = ⌈(height − bar) ÷ lift⌉ + 1, each lapping the one below by bar − lift, with the top piece cut to fit.Source
• Lap length: 48 bar diameters for Grade 60 (#4 = 24", #5 = 30", #6 = 36")The IBC 2107.2 alternative for allowable stress design, as summarized by ENERCALC: 40 diameters for 40 ksi bars, 48 for 60 ksi. The TMS 402 development-length equation (Eq. 6-1) depends on masonry strength, cover and bar size and often gives longer laps (up to 72 diameters) — use the lap on your structural drawings when it is given.Source
• TMS 402 lap equation: ld = 0.13 × db² × fy × γ ÷ (K × √f′m), at least 12"; γ = 1.0 (#3–#5), 1.3 (#6–#7), 1.5 (#8+)Masonry Advisory Council summary of TMS 402. K is the smallest of the cover, the clear spacing between splices and 9 db. Not computed here — it needs f′m and cover from the design.Source
• Drill-in dowels: One per vertical bar; length = embedment (4" default) + one lap above the slab or footingThe first vertical bar laps the dowel. The embedment is your engineer's or the adhesive report's number — 4" is only the default; adhesive makers list minimum embedments per bar size (e.g. Hilti HIT-HY 200 V3: #4 2¾", #5 3⅛", #6 3½").
• 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): #4 0.668 · #5 1.043 · #6 1.502 · #7 2.044 · #8 2.670 lb/ftThe same table the rebar calculator uses: bar area × 3.40 lb/ft per in².Source
• Stock bars: Lapped bars use full stock pieces plus a cut piece; lift bars and cut pieces are packed into stock bars longest firstOffcuts that fit another cut piece are reused — three 6'8" lift bars come out of one 20' bar. Waste, if entered, is added to the stock bar count only.