Stone calculator
Stone Wall Mortar Calculator
Enter the wall face area and joint style to get mortar bags, sand tonnage and the right mix type.
Your project
Mortar needed
67
80 lb bags of type N premix
- Joint volume
- 40 cu ft
- If mixing from scratch — portland
- 20.1 bags (94 lb)
- If mixing from scratch — sand
- 2.01 tons
- Cement : lime : sand ratio
- 1 : 1 : 6
- Estimated mortar cost
- $737
Mix only what you can lay in about 90 minutes. Mortar that has started to set cannot be retempered with more water without losing most of its strength.
The shareable link reopens this calculator with your exact inputs.
Choosing the mortar type
Type N is the default for above-grade stone work: 750 psi, flexible enough to absorb small movements, and soft enough that it fails before the stone does. Type S at 1,800 psi is used below grade, for retaining work and for veneer.
Harder is not better. A high-strength mortar around soft sandstone or historic brick transfers stress into the units, and the stone spalls instead of the joint. Match the mortar to the stone, not to the highest number on the shelf.
How much mortar a stone wall actually takes
Joints in rubble stone masonry occupy about a quarter of the wall volume — far more than the 7-10% in brickwork, because the stones do not sit flush. Irregular field stone can reach 35%.
One 80 lb bag of premixed mortar yields roughly 0.6 cubic feet of mortar. From scratch, the same yield needs about 0.3 bags of portland, a scoop of lime and 60 lb of masonry sand.
Mortar types
| Type | Strength | Mix (C : L : S) | Use |
|---|---|---|---|
| Type N | 750 psi | 1 : 1 : 6 | Above-grade stone and brick |
| Type S | 1,800 psi | 1 : 1/2 : 4.5 | Below grade, veneer, retaining |
| Type M | 2,500 psi | 1 : 1/4 : 3 | Heavy load, foundations |
| Type O | 350 psi | 1 : 2 : 9 | Historic and soft stone repointing |
Frequently asked questions
+How many bags of mortar for a stone wall?
Roughly one 80 lb bag per 2.5 cubic feet of wall volume in rubble stone work. A 120 sq ft face at 16 inches thick needs about 67 bags.
+What mortar should I use for a stone wall?
Type N above grade, type S below grade or for veneer and retaining walls. Use type O for repointing soft historic stone.
+How much sand per bag of cement?
For type N, six parts sand to one part portland and one part lime by volume — about 60 lb of masonry sand per 0.6 cubic feet of finished mortar.
+Can I use concrete mix instead of mortar?
No. Concrete contains coarse aggregate that prevents the joint from tooling and bonding properly, and it is far too rigid for stone joints.