Mortar Mix Calculator

Mortar mix calculator for cement, sand, water, and bag quantities

Mortar is the workable paste used to bond bricks, blocks, and stone. The part that usually goes wrong in real projects is not the ratio, it is the quantity. People under-buy and end up with inconsistent batches, or they over-buy and waste cement and sand. This mortar mix calculator turns a target mortar volume into an itemized estimate of cement and sand, plus a practical water estimate and the number of cement bags to buy.

The starting point is the mortar volume you want to produce. Many users think in liters because they are mixing in a wheelbarrow, mixer, or buckets, so you can enter liters directly. If you are planning at a bigger scale, you can enter cubic meters instead. From there, choose a cement to sand ratio such as 1:4, 1:5, or 1:6. These ratios describe the dry ingredients by volume, which is how mortar is commonly proportioned on site.

This calculator also supports the reality that the wet mortar you apply is not the same as the dry ingredient volume you measure. When you mix and compact mortar, you lose volume to voids and packing. That is why a “dry factor” is included. If you are in a hurry, leave all advanced fields blank and you will still get a useful estimate based on common defaults. If you want to be more precise for your local materials and mixing method, you can adjust waste, densities, dry factor, bag size, and water ratio.

Assumptions and how to use this calculator

• Mix ratios are treated as dry volume parts (cement : sand) and are applied to the calculated dry ingredient volume.
• Default dry factor is 1.33, meaning dry ingredients are estimated as 1.33× the target wet mortar volume to account for compaction and voids.
• Default cement density is 1,440 kg/m³ and default sand density is 1,600 kg/m³. Real values vary by brand, moisture, and grading.
• Water is estimated using a default water to cement ratio of 0.50 by weight. Actual water needed depends on sand moisture and desired workability.
• Waste is applied as a simple percentage uplift to the target wet volume. It covers spillage, rework, and handling losses, not structural design issues.

Common questions

What does the mix ratio (1:4, 1:5, 1:6) actually mean?

It means one part cement to four, five, or six parts sand by volume before adding water. A richer mix (like 1:4) uses more cement and can be stronger, while a leaner mix (like 1:6) uses less cement and is often used where very high strength is not required. Your building code, engineer, or supplier should define what is appropriate for your use case.

Why does the calculator use a “dry factor” and not just split my wet volume by the ratio?

Because wet mortar volume is smaller than the loose dry ingredient volume you measure into a mixer or wheelbarrow. Dry materials pack together and fill voids, so the combined wet volume is not a simple sum. The dry factor is a practical way to estimate the extra dry volume needed to end up with the wet mortar you want. If you have historical site data, adjust the dry factor to match your outcomes.

How many cement bags should I buy: exact bags or rounded up?

Buy rounded up. The “exact bags” number is a math result, but you cannot buy fractions of a bag. Round up to the next whole bag, then plan to use leftover cement quickly and store it dry. If you are mixing across multiple days, rounding up also reduces the risk of batch-to-batch variation caused by running short.

My sand is damp. Will that change the result?

Yes. Damp sand is heavier per cubic meter and already contains water, so you may need less added water for the same workability. The calculator’s sand density and water estimate are defaults that assume typical bulk conditions. For better accuracy, use a sand density that matches your stockpile and reduce the water ratio slightly if your sand is visibly wet.

Can I use this for plaster, screed, or concrete?

Use it cautiously. Plaster and screed mixes may use different ratios, additives, and workability targets, and concrete includes coarse aggregate, which changes everything. This calculator is designed for cement-and-sand mortar. If you are working with concrete or a specialized product, use a dedicated calculator or follow the manufacturer’s mix design guidance.