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Sources & method

Every constant the calculators use, where it came from and when it was last checked. Figures reviewed October 1, 2026.

The numbers

WhatValueFrom
Pre-mixed concrete yield40 lb 0.30 ft³ · 50 lb 0.375 · 60 lb 0.45 · 80 lb 0.60Quikrete and Sakrete data sheets
Normal-weight concrete140–150 lb/ft³ (145 used as the midpoint)NRMCA CIP 36
Structural lightweight concrete90–120 lb/ft³NRMCA CIP 36
Default extra10% (NRMCA range 4–10%)NRMCA CIP 8; Sakrete
Rebar #3 / #4 / #5 / #60.376 / 0.668 / 1.043 / 1.502 lb/ftASTM A615 via Caltrans
Lap length40 bar diameters (Grade 40) or 60 (Grade 60)IRC Table R608.5.4(1) via Element ICF
Concrete block coverage1.125 blocks per ft² (8×8×16)Martinsville Concrete
Mortar12 (Sakrete) or up to 13 (Quikrete) blocks per 80 lb bagSakrete; Quikrete
Stairs7¾ in maximum riser, 10 in minimum treadIRC R311.7.5
Evaporation bands0.5 and 1.0 kg/m²/h (0.1 and 0.2 lb/ft²/h)Menzel/Bloem via Kestrel
Default bag price$6.47 per 80 lb bagOne US home center, October 2026
Default ready-mix price$180 per cubic yardConcreteNetwork, 2025 US average

How the calculators are tested

The formulas live in a small library with automated tests. The tests check results against published figures: Sakrete’s bags-per-post-hole chart, Quikrete’s Quik-Tube and post-setting examples, Sonoco’s per-foot tube volumes, the IRC lap-splice table, and a cross-check between the metric and English forms of the evaporation equation.

All sources

  1. Quikrete — Concrete Mix No. 1101 — technical data sheet (bag yields, strength gain, curing) · checked October 1, 2026
  2. Sakrete — High-Strength Concrete Mix — technical data sheet · checked October 1, 2026
  3. Sakrete — Estimating bagged concrete jobs · checked October 1, 2026
  4. Quikrete — Fast-Setting Concrete Mix No. 1004 — technical data sheet · checked October 1, 2026
  5. Sakrete — Fast-Setting Concrete Mix — technical data sheet (bags per post hole) · checked October 1, 2026
  6. Quikrete — Setting posts — project instructions · checked October 1, 2026
  7. Quikrete — Quik-Tube building form — data sheet · checked October 1, 2026
  8. Sonoco — Sonotube Builder’s Tube concrete forms — specification sheet · checked October 1, 2026
  9. National Ready Mixed Concrete Association — CIP 8 — Discrepancies in yield (ordering 4–10% extra) · checked October 1, 2026
  10. National Ready Mixed Concrete Association — CIP 36 — Structural lightweight concrete (unit weights) · checked October 1, 2026
  11. National Ready Mixed Concrete Association — CIP 5 — Plastic shrinkage cracking (precautions) · checked October 1, 2026
  12. National Ready Mixed Concrete Association — CIP 11 — Curing in-place concrete · checked October 1, 2026
  13. Kestrel Instruments — How to prevent plastic shrinkage cracks (Uno evaporation equations and risk bands) · checked October 1, 2026
  14. Caltrans — Bridge Design Details, ch. 13 — ASTM A615 bar sizes, areas and weights · checked October 1, 2026
  15. Element ICF — TB-4 Lap splices (IRC Table R608.5.4(1) values for Grade 40 and Grade 60) · checked October 1, 2026
  16. Dayton Superior — Rebar splicing handbook — tabulated ACI 318 lap lengths · checked October 1, 2026
  17. Martinsville Concrete — Masonry estimating guide (8×8×16 block, 1.125 blocks per sq ft) · checked October 1, 2026
  18. Quikrete — Mortar Mix No. 1102 — technical data sheet (blocks per bag) · checked October 1, 2026
  19. Sakrete — Mortar Mix Type S (blocks per bag) · checked October 1, 2026
  20. Stairbuilders and Manufacturers Association — IRC R311.7.5.1 risers (7¾ in maximum) — 2021 IRC commentary · checked October 1, 2026
  21. State of Ohio (adopted IRC text) — Residential Code of Ohio 4101:8-5-01 — R506.1 concrete floors on ground (3½ in minimum) · checked October 1, 2026
  22. State of Ohio (adopted IRC text) — Residential Code of Ohio 4101:8-4-01 — Table R402.2 minimum compressive strength; R403.1.4 footing depth · checked October 1, 2026
  23. Ohio Ready Mixed Concrete Association — Guidelines for durable driveways, patios and walks · checked October 1, 2026
  24. Michigan Concrete Association — Driveway and sidewalk guidelines · checked October 1, 2026
  25. ConcreteNetwork.com — Concrete prices — national ready-mix average ($179.95 per cubic yard, 2025) · checked October 1, 2026
  26. The Home Depot — Quikrete Concrete Mix, 80 lb — shelf price at one US store · checked October 1, 2026
  27. Quikrete — QUIKRETE 5000 Concrete Mix No. 1007 — technical data sheet · checked October 1, 2026
  28. Sakrete — 5000 Plus Concrete Mix — product page · checked October 1, 2026
  29. Sakrete — High-Strength Concrete Mix — product page (foot and vehicle traffic times) · checked October 1, 2026
  30. US Bureau of Labor Statistics via FRED — Producer Price Index: ready-mix concrete manufacturing (PCU327320327320) · checked October 1, 2026
  31. Federal Highway Administration — FHWA-HRT-05-038 — Curing durations summarised from ACI 308 and ACI 301 · checked October 1, 2026

Corrections log

No corrections yet. Confirmed corrections are listed here with the date and what changed.