Methods & sources

How the numbers are made

cu ft = length × width × thickness (in) ÷ 12; cu yd = cu ft ÷ 27
bags = round up(cu ft × (1 + margin) ÷ the maker's yield per bag)
tube = π × (diameter in ÷ 24)² × length ft; post hole = (π × hole² ÷ 4 − post area) × (depth − gravel − top gap) ÷ 1,728
tons = cu yd × the published tons-per-yard range (low to high)

The same code runs in your browser and in our build. It is tested against the makers' own worked figures: 27 ÷ 0.60 = 45 bags of 80 lb Quikrete per yard, Quikrete's own slab and post-hole formulas, Sakrete Maximizer's 2.75 sq ft at 4 in, Sonoco's charts (within 1% of π r² h) and the extension services' 324 sq ft per yard at 1 in.

How the data is checked

A program reads every yield, water amount, density and chart value out of the cached maker, government and extension documents below. The site does not build unless each figure is found word for word in its document (92 quotes checked), and Quikrete's yields must agree across its data sheet, SPEC-DATA sheet and calculator code. Single-source figures and disagreements were reviewed by hand:

• qcm 90 lb: yield 0.675 cu ft from one maker document only (qk_concretemix_tds2)
  90 lb bag is on the current Concrete Mix data sheet ('regional availability'); the SPEC-DATA sheet and calculator.js predate it. Same maker document as the four sizes that the second sources confirm; consistent with them (0.675 = 90/80 x 0.60).
• qfs 60 lb: yield 0.45 cu ft from one maker document only (qk_fastsetting_tds2)
  60 lb Fast-Setting yield from the current maker data sheet; the 50 lb yield on the same sheet is confirmed by calculator.js. 0.45 = 60/50 x 0.375, consistent.
• shs 40 lb: yield 0.3 cu ft from one maker document only (sakrete_highstrength_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• shs 60 lb: yield 0.45 cu ft from one maker document only (sakrete_highstrength_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• shs 90 lb: yield 0.66 cu ft from one maker document only (sakrete_highstrength_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• s5k 50 lb: yield 0.38 cu ft from one maker document only (sakrete_5000plus_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• s5k 60 lb: yield 0.47 cu ft from one maker document only (sakrete_5000plus_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• s5k 80 lb: yield 0.6 cu ft from one maker document only (sakrete_5000plus_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• smx 40 lb: yield 0.46 cu ft from one maker document only (sakrete_maximizer_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• smx 80 lb: yield 0.92 cu ft from one maker document only (sakrete_maximizer_tds)
  Maker's own technical data sheet (current PDF on sakrete.com, linked from its technical-documents page). Sakrete publishes no second yield table we can fetch; the site shows it as the maker's published yield with the sheet's date.
• smx 80 lb: sakrete_maximizer_page says 3.0 sq ft at 4 in; 0.92 cu ft gives 2.76 (8% apart)
  The product page rounds coverage to '3 sq. ft.'; the data sheet says 2.75 sq ft, which matches 0.92 cu ft / (4/12 ft) = 2.76. The site uses the data-sheet yield (0.92) and never the rounded page figure.
• density topsoil: sources differ by 60% (0.8 to 1.2825 t/yd3); shown as a range
  Real spread between sources (loose vs packed vs wet soil, and the NM factor is for mine production reporting). The site never shows one figure: tons are a range with each source listed and the line 'ask your supplier for their tons per yard'.
• density fill: 0.8 t/yd3 from one source only (nm_emnrd_convfactors)
  Only the New Mexico EMNRD factor is published by a public body among the sources we fetched. Shown as 'about 0.8 tons per yard (one source)' with an ask-your-supplier line.
• density base: 1.25 t/yd3 from one source only (nm_emnrd_convfactors)
  Only the New Mexico EMNRD base-course factor among fetched public sources. Shown labelled as one source, with an ask-your-supplier line; gravel/crushed stone (5 sources) is the default material.
• gravel bag 0.5 cu ft / 50 lb from a retailer listing only (truevalue_gravel)
  Quikrete's own gravel page states the 50 lb bag but not its volume; the retailer listing gives the product's printed name '0.5 Cu. Ft. 50 Lb.'. Used only for the bag count of 50 lb gravel bags; users can change the bag size.
• post rule: Quikrete's three documents word the hole depth differently (guide 1/3-1/2 of above-ground length + 6 in; data sheet 1/3 of overall height; calculator 1/2 of above-ground height); the site lets the user enter depth and shows the guide's range
  Reviewed: the site does not pick a depth for the user. Hole width uses the 3x rule (all three documents agree), depth is the user's input, and the guide's 1/3-1/2 + 6 in range is shown as a helper with all three wordings quoted on the post page.

An automated job re-downloads the maker data sheets each month and flags any change for review before it reaches the site.

What we don't do

We don't size footings, piers, slabs or rebar, and we make no claim about strength, codes or what a structure can carry. We show no prices: every cost comes from prices you type. Product names identify the source of a published figure; ConcreteMath isn't affiliated with any maker or store, and products we track are not all brands on the market.

Sources

• Quikrete: QUIKRETE Concrete Mix (No. 1101) data sheet (maker) · fetched and reviewed 2026-11-10
• Quikrete: QUIKRETE Concrete Mix SPEC-DATA sheet (maker) · fetched and reviewed 2026-11-10
• Quikrete: QUIKRETE online project calculator (calculator.js) (maker) · fetched and reviewed 2026-11-10
• Quikrete: QUIKRETE Fast-Setting Concrete Mix (No. 1004-50) data sheet (maker) · fetched and reviewed 2026-11-10
• Quikrete: QUIKRETE guide: Setting Posts in Concrete (maker) · fetched and reviewed 2026-11-10
• Quikrete: QUIKRETE project calculator page (maker) · fetched and reviewed 2026-11-10
• Sakrete: Sakrete High Strength Concrete Mix technical data sheet (maker) · fetched and reviewed 2026-11-10
• Sakrete: Sakrete 5000 Plus Concrete Mix technical data sheet (maker) · fetched and reviewed 2026-11-10
• Sakrete: Sakrete Maximizer Concrete Mix technical data sheet (maker) · fetched and reviewed 2026-11-10
• Sakrete: Sakrete Maximizer product page (maker) · fetched and reviewed 2026-11-10
• Sonoco: Sonotube Builder's Tube concrete forms (concrete chart) (maker) · fetched and reviewed 2026-11-10
• Sonoco: Sonotube Round concrete forms brochure (concrete requirements table) (maker) · fetched and reviewed 2026-11-10
• True Value: Quikrete All-Purpose Gravel 50 lb listing (retailer) (maker-retail) · fetched and reviewed 2026-11-10
• New Mexico EMNRD (Mining and Minerals Division): Conversion factors for construction materials and common minerals (gov) · fetched and reviewed 2026-11-10
• Nebraska DOT: Estimating material quantities (gov) · fetched and reviewed 2026-11-10
• Two Rivers-Ottauquechee Regional Commission (Vermont): Material weight, pounds per cubic yard (from EPA & NTEA) (gov) · fetched and reviewed 2026-11-10
• Ask Extension (Cooperative Extension): How much soil for raised beds (extension) · fetched and reviewed 2026-11-10
• University of Florida IFAS Extension: Mulch (Gardening Solutions) (extension) · fetched and reviewed 2026-11-10
• Colorado State University Extension: Mulches for home gardens (extension) · fetched and reviewed 2026-11-10
• Iowa State University Extension: How to determine the amount of mulch needed (extension) · fetched and reviewed 2026-11-10
• UC Marin Master Gardeners: Applying mulch (extension) · fetched and reviewed 2026-11-10
• NRMCA: CIP 31: Ordering Ready Mixed Concrete (industry) · fetched and reviewed 2026-11-10

Change log

• 2026-11-10: launch data fetched and reviewed (15 bag sizes in 5 products, 14 density figures, 2 Sonotube charts).

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