Mortar Mix Calculator (Type N / S / M / O)
Mortar volume + ASTM C270 type → Portland cement, hydrated lime, and sand quantities by proportion.
Result
- Wet mortar volume10 ft³
- Dry-volume factor×1.27 (PCA bulking allowance)
- Mix ratio (cement:lime:sand)1 : 1 : 5.5
- Cement1.69 ft³ = 2 × 94-lb bag
- Hydrated lime1.69 ft³ = 2 × 50-lb bag
- Sand9.31 ft³ = 0.345 yd³
- Min 28-day strength750 psi (ASTM C270)
Step-by-step
- Dry volume = 10 × 1.27 = 12.70 ft³ (sand packs ~⅔ of dry volume).
- Cement = 12.70 × 1 / 7.50 = 1.69 ft³.
- Lime = 12.70 × 1 / 7.50 = 1.69 ft³.
- Sand = 12.70 × 5.5 / 7.50 = 9.31 ft³.
How to use this calculator
- Enter the wet mortar volume in ft³ (typically computed from masonry-unit count + joint volume).
- Pick the ASTM C270 type — Type N is the all-purpose choice.
- Read cement bags, lime bags, and sand cubic yards needed.
About this calculator
ASTM C270 defines four mortar types — M, S, N, O — by Portland cement / hydrated lime / sand proportions and minimum 28-day compressive strength. Type M (2500 psi) is for load-bearing masonry below grade; Type S (1800 psi) for above-grade structural; Type N (750 psi) is the general-purpose default for above-grade veneers and partitions; Type O (350 psi) is the soft historic-repointing mix for interior non-load-bearing work. The 1.27 dry-volume multiplier accounts for the void space sand fills around cement and lime.
What this calculator does
This calculator returns the Portland cement, hydrated lime, and sand quantities (in cubic feet, bags, and cubic yards) needed to mix a given volume of mortar at one of the four ASTM C270 mortar types (M, S, N, O). Proportions come directly from C270 Section 8.1 (proportion specification); volumes use the standard 1.27 dry-bulking multiplier published by the Portland Cement Association.
How it works — the formula
dry_volume = wet_volume × 1.27
for each ingredient: dry_volume × proportion / sum_of_proportions
Proportions (cement:lime:sand) per ASTM C270:
Type M 1 : ¼ : 3⅜ (avg)
Type S 1 : ½ : 4¼
Type N 1 : 1 : 5½
Type O 1 : 2 : 8¼ASTM C270 publishes proportion specifications by mortar type. Wet-to-dry volume bulking allows for the fact that sand voids absorb the cementitious paste, so dry ingredients sum to ~1.27× the wet mortar volume produced. Bag conversions use the standard 94-lb (= 1 ft³) cement bag and 50-lb (= 1.25 ft³) hydrated-lime bag.
Worked examples
- Inputs:
- V=10 ft³, type=N (1:1:5.5)
- Output:
- ~2 × 94-lb cement + ~2 × 50-lb lime + ~0.32 yd³ sand
Typical patio brick wall mortar quantity.
- Inputs:
- V=20 ft³, type=S (1:½:4.25)
- Output:
- ~5 × cement + ~3 × lime + ~0.66 yd³ sand
Earthquake-zone above-grade block wall.
- Inputs:
- V=5 ft³, type=M (1:¼:3.375)
- Output:
- ~2 × cement + ~1 × lime + ~0.17 yd³ sand
Foundation parging — high-strength below-grade mortar.
When to use this vs other tools
Use this for site-mixed mortar quantities. For pre-blended bagged mortar, the bag-yield tool converts coverage directly.
- Mortar Bag Yield
Use to convert ft³ of mortar into Quikrete / Sakrete bag counts for pre-blended product.
- Brick Count for Wall
Use to compute the upstream brick count and joint volume that determines mortar quantity.
- Concrete Volume
Use for concrete pours (different mix; mortar is masonry-only).
- Stucco Coverage
Use for the related stucco-mix application; mortar and stucco share cement+lime+sand bases.
Authority note
ASTM C270 is the standard specification referenced by every US masonry building code. Proportion specifications and minimum 28-day compressive strengths come directly from C270 Tables 1 and 2. PCA publishes the 1.27 wet-to-dry bulking factor used here.
Limitations
- Uses proportion specification (Section 8.1); property specification (Section 8.2) requires lab-tested strength rather than ratios.
- Sand range in ASTM C270 is 2.25-3× (cement + lime); we use the midpoint. Tight-spec jobs should use the lower end.
- Doesn't account for additives (latex, color, set retarder) that may displace some volume.
- For commercial masonry, proportion-spec mortars must use ingredients matching ASTM C150 (cement) and ASTM C207 (hydrated lime).
For structural masonry, mortar mix must comply with the project specifications; consult a structural engineer and follow ASTM C270 testing requirements.