Formula and method
Country presets are starting examples, not building-code approval. Catalogue dimensions can be nominal: the laying module includes the joint, while actual dimensions exclude it. Gulf examples use a 400 × 200 mm module with assumed 390 × 190 mm actual units; the French example uses a 500 × 200 mm module with assumed 490 × 190 mm units. Confirm actual measurements before estimating mortar. The Australian brick and block sizes and Swedish LECA example are taken from the linked references.
For site-mixed mortar, the default 1:0:4 cement:lime:sand volume ratio, 1.33 dry factor, 1,440 kg/m³ cement bulk density, 5% unit waste and 10% mortar allowance are editable planning assumptions, not prescribed grades. Confirm the specified cement/lime/sand mix. For factory mortar, 13 L per 20 kg bag is an illustrative yield only. Replace it with the manufacturer’s wet yield. Do not break proprietary adhesive or premixed mortar into invented cement and sand quantities.
Joint volume uses the outer block envelope, not its solid-material fraction. The default factor 1 assumes full-width filled joints; adjust only from the actual bedding specification. It is not a hollow-core percentage. Hollow cores, reinforcement grout, lintels, ties, DPC, insulation, cavity, plaster, foundations and structural design are excluded. The wall envelope shown includes block voids and is not a concrete order.
Formula and method
Net area equals length × height minus openings. Units equal net area × identical leaves divided by the laying-module face area. Joint mortar equals net area × leaves × leaf thickness × [1 − actual face area/module face area] × bedding factor. This periodic joint model is approximate at boundaries and cuts. Add separately measured additional mortar once; do not double-count joints already included. Round purchase quantities upward after allowances.
Dry volume equals wet site mortar × dry factor. Cement mass equals dry volume × cement volume share × cement bulk density. Sand and lime are loose dry volumes. Factory bags equal wet litres divided by litres per bag. Thin-bed mass equals net area × leaves × product kg/m²; allowance is then applied. Additional leveling mortar in thin-bed mode is calculated separately as a site mix. Its allowance is applied once.
L,H,ML,MH,BL,BH,T → m; A,O → m² A = L × H − O N = A × n / (ML × MH) V = A × n × T × [1 − (BL × BH)/(ML × MH)] × f Vwet = (V + Vextra) × (1 + wm/100) Vdry = Vwet × k Mc = Vdry × c/(c + l + s) × ρc Vs = Vdry × s/(c + l + s) Mthin = A × n × q × (1 + wm/100) Norder = ceil[N × (1 + wu/100)]
Example dimensions describe one rectangular wall. Combine walls only when height, system and openings are compatible; enter the summed length and opening area. Two identical leaves double masonry quantity but do not include the cavity. Feet input applies to length/height and ft² to openings; block sizes stay in mm and outputs use SI. Changing units converts existing measurements. Calculations run in your browser; a downloaded record contains the inputs you entered. References reviewed 23 October 2026; supplier specifications can change.