Calculate bags of sand and cement needed for bricklaying
Getting the right amount of mortar is just as important as getting the right number of bricks. Too little mortar means stopping work mid-project to make another trip to the builders' merchant, while too much means wasted materials and money. Mixed mortar has a limited working life (typically 1-2 hours depending on conditions), so it is also important not to mix more than you can use in a session. This mortar calculator estimates the total weight of mortar needed for a given number of bricks, then breaks it down into the quantities of sand and cement required based on your chosen mix ratio. It calculates the number of bags you need to purchase, rounding up to whole bags since you cannot buy partial bags. The calculator supports the three most common mortar mix ratios used in UK construction: 4:1 for standard bricklaying, 3:1 for stronger rendering and below-ground work, and 5:1 for general-purpose and non-structural applications.
To calculate mortar quantities: 1. Enter the number of bricks you plan to lay. If you have already used the brick calculator, use the "Bricks with Waste" figure from that result for consistency. 2. Select the mix ratio. For standard domestic bricklaying, 4:1 (sand to cement) is the most common. Choose 3:1 for rendering or below-damp-proof-course work. Choose 5:1 for pointing or non-structural applications. 3. Select the cement bag size. Standard UK bags are 25kg, though 20kg bags are increasingly common at retail outlets and are easier to handle. 4. Select the sand bag size. Building sand is available in 25kg bags from DIY stores, or in bulk bags (800-1000kg) for larger projects. 5. Review the results showing total mortar weight, individual material weights, and the number of bags to purchase. For large projects, consider ordering sand in bulk (by the tonne) rather than in bags for significant cost savings.
The mortar calculation uses the industry-standard estimate of approximately 1kg of mortar per standard UK brick: Total Mortar (kg) = Number of Bricks x 1 For a given mix ratio (e.g., 4:1 sand to cement), the total parts are sand parts + cement parts: Cement Weight (kg) = Total Mortar x Cement Parts / Total Parts Sand Weight (kg) = Total Mortar x Sand Parts / Total Parts For example, 500 bricks with a 4:1 mix: total mortar = 500kg, total parts = 5, cement = 500/5 = 100kg, sand = 500 x 4/5 = 400kg. Cement Bags = ceiling(Cement Weight / Bag Size) Sand Bags = ceiling(Sand Weight / Bag Size) With 25kg bags: cement bags = 100/25 = 4, sand bags = 400/25 = 16. The 1kg-per-brick rule assumes standard 10mm bed and perpend joints with a standard UK brick. For thicker joints or non-standard bricks, adjust the total mortar estimate proportionally.
Mortar should be mixed in small batches and used within 1-2 hours in warm weather, or up to 3 hours in cool conditions. Never re-temper (add water to) mortar that has started to set. For consistent results, use a gauging box or bucket to measure materials by volume before mixing. In cold weather (below 5 degrees Celsius), use frost-proofer additive or delay work until temperatures rise. All mortar for structural work should comply with BS EN 998-2 and the recommendations in PD 6678.