Sources
Every external source behind our calculators, what it is used for, and its limits.
Used in calculations
The only external values that enter calculations automatically.
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NIST Guide to the SI (SP 811), Appendix B.8 — Factors for units listed alphabetically
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Scope: Unit conversion (length) — 1 in = 0.0254 m; 1 ft = 0.3048 m; 1 yd = 0.9144 m
Limitations: International foot, not the US survey foot.
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Scope: Unit conversion (area and volume) — 1 ft² = 0.09290304 m²; 1 ft³ = 0.02831685 m³; 1 yd³ = 0.7645549 m³; exactly 27 ft³ per yd³
Limitations: Published factors are rounded to displayed precision; exact values follow from the foot and yard definitions.
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Scope: Unit conversion (mass and density) — 1 US short ton = 2,000 lb = 907.1847 kg; 1 metric tonne = 1,000 kg; 1 US short ton/yd³ = 1,186.553 kg/m³; 1 lb/ft³ = 16.01846 kg/m³
Limitations: US short ton, long ton and metric tonne are distinct. Long tons are not exposed in the interface.
Pages: All calculators
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Educational references you can choose
Used only when you explicitly select them.
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Proper Concrete Paver Base and Depth: What to Know and Why It Matters
Used as an educational reference you can choose:
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Scope: Conventional interlocking concrete pavers — pedestrian, under ideal conditions — Minimum 4 in (100 mm) base, pedestrian, under ideal conditions
Limitations: Under ideal conditions only. Weak soils, poor drainage and freezing require more. Not for permeable pavers or gravel-surfaced driveways.
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Scope: Conventional interlocking concrete pavers — residential driveway, under ideal conditions — Minimum 6 in (150 mm) base, residential driveway, under ideal conditions
Limitations: Under ideal conditions only. Weak soils, poor drainage and freezing require more. Not for permeable pavers or gravel-surfaced driveways.
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Scope: Conventional interlocking concrete pavers — parking lot / residential street, under ideal conditions — Minimum 8 in (200 mm) base, parking lot / residential street, under ideal conditions
Limitations: Under ideal conditions only. Weak soils, poor drainage and freezing require more. Not for permeable pavers or gravel-surfaced driveways.
Also used as explanatory context:
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Scope: Conventional interlocking concrete paver base — material suitability and unfavorable-condition guidance — +50% of ideal minimum per unfavorable condition (rough estimate); use locally approved road-base aggregate or DGA close to ASTM D2940; avoid smooth pea gravel/river rock, screenings and excessive fines
Limitations: CMHA calls the adjustment a quick estimate; it is never applied automatically.
Pages: Paver Base Calculator, Pea Gravel Calculator, River Rock Calculator, Road Base Calculator, Crushed Stone Calculator
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Explanatory context
Cited in guidance to explain scope and limits. Never used as calculator values.
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Alternative Backfills for Highway Applications: State of the Practice (FHWA-HRT-23-110), Table 7
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Scope: Highway backfill — ordinary fills, loose (ASTM C29) — 1,425–1,680 kg/m³ (typical design values for ordinary fills, loose)
Limitations: Not a tested range for any named gravel product.
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Scope: Highway backfill — ordinary fills, compacted in place, moist — 1,600–2,080 kg/m³ (compacted in-place, moist)
Limitations: Different condition from the loose range above; must not be paired with it to derive a compaction factor.
Pages: Gravel Calculator, Gravel Weight Calculator, Gravel Tons-to-Yards Calculator
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Gravel Roads: Construction and Maintenance Guide (FHWA-OTS-15-0002), Appendix A Table 3
Scope: Reconstructed rural gravel roads, by heavy-truck traffic and subgrade support — 115, 140 or 165 mm (4.5, 5.5 or 6.5 in) for 0–5 heavy trucks/day; up to 370 mm (14.5 in) for 25–50 heavy trucks/day with low support
Limitations: Not a residential driveway section. Never fills a driveway depth.
Pages: Gravel Driveway Calculator, Road Base Calculator, Crusher Run Calculator
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Unpaved Roads Chemical Treatments, Chapter 6
Scope: Wearing course for treated unpaved roads — At least 4 in (100 mm), preferably 6 in (150 mm)
Limitations: For treated unpaved roads; not a decorative bed, top-up or private-driveway default.
Pages: Gravel Driveway Calculator, Road Base Calculator
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Watering Systems for Serious Graziers, p. 37
Scope: Spring-collection French drain for livestock watering — 4 in PVC pipe and 1 in clean rock (example); publication date not verified (file hosted 2023)
Limitations: Specific grazing/spring-collection design; not a household trench, width, depth or pipe specification.
Pages: French Drain Gravel Calculator
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Gravel Drainage Specifications
Scope: Sand-based sports-field drainage — 4 in minimum pipe; trench at least 6 in wide/deep; at least 1 in gravel under pipe; gravel blanket at least 4 in
Limitations: Sports-field system; not a home French drain.
Pages: French Drain Gravel Calculator
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Hydraulic Performance of Shallow Foundations… (FHWA-HRT-17-013), Chapter 3
Scope: Engineered riprap aprons at bridge foundations — Thickness max(D100, 1.5 × D50)
Limitations: Applies after hydraulic sizing; not a consumer default.
Pages: Riprap Quantity Calculator
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HEC-RAS Riprap Calculator: Rock Size and Weight Specifications (v6.1 documentation)
Scope: Riprap gradation and layer thickness — Layer thickness max(d100, 1.5 × d50)
Limitations: Depends on design flow, stone source and gradation. Rock particle weight is not bulk order density.
Pages: Riprap Quantity Calculator
Methodology
Standards that define the measurements this site relies on.
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ASTM C29/C29M-17a — Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
Scope: Bulk-density measurement methodology
Limitations: Methodology only; no value from it is used in calculations.
Pages: All calculators
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ASTM C127-25 — Relative Density (Specific Gravity) and Absorption of Coarse Aggregate
Scope: Particle relative density methodology
Limitations: Particle relative density is not bulk density and is never used to convert volume to weight.
Pages: Gravel Calculator, Gravel Weight Calculator, Gravel Tons-to-Yards Calculator, Limestone Calculator, Crushed Stone Calculator
Reviewed but not used
We also reviewed supplier product calculators that publish a single weight-per-yard figure. Their test conditions, location and moisture were not stated, the same figure appeared across very different products, and one listed an impossible zero density. We do not use them for any calculation or recommendation.
Broad ordinary-fill density ranges from highway research are cited only as context: they describe highway backfill, not any named gravel product.