Calculators

34 articles

• Brickwork Quantity Calculator: Bricks per M2, Mortar Mix Ratios and Waste Allowances
• BTU to kW Conversion: Quick Reference for Heating Engineers
  BTU to kW conversion table, radiator output reference, room heat loss calculation method (1 kW = 3,412 BTU/h)
• Cable Voltage Drop Calculator: How to Check Your Circuits Comply
  Cable voltage drop calculator: BS 7671 mV/A/m values, 3%/5% limits, worked examples for ring final, shower, cooker circuits
• Concrete Mix Ratios: Foundations, Posts, Floor Slabs and Structural Mixes Explained
• Concrete Volume Calculator: Slabs, Footings & Mix Ratios
  Concrete volume calculator: L×W×D formula with 10% waste, C20/C25/C30 mix ratios (1:2:4 = C20), worked examples for patio, strip footing, fence posts, trench fill
• Drainage Pipe Sizing Calculator: Flow Rates, Gradients and BS EN 752 Design Method
• External Render Quantity Calculator: Coverage per Bag for Scratch Coat, Float and Finish
• Fence Post Depth Calculator: Depth Rules, Post Sizing and Concrete vs Driven Installations
  Fence post depth calculator: one-third rule + 150mm (750mm for 1.8m fence), 100×100mm post for 1.8m fence, 300mm minimum concrete collar diameter, BS 8417 UC4 pressure treatment, GPDO 2015 height limits
• Gravel and Aggregate Quantity Calculator: Tonnes per M2 by Depth and Material Type
• Grout Quantity Calculator: Tile Size, Joint Width & Coverage
  Grout quantity calculator: formula with worked examples for 300×300mm floor, 600×600mm large format, and mosaic tiles
• Heat Pump Radiator Output Correction Calculator: Delta-T Correction Factors, MCS Heat Emitter Guide Method and Worked Examples
  Delta-T correction factors from BS EN 442, MCS Heat Emitter Guide method, worked example 35/30°C flow/return vs 70/50°C rated, correction factor tables by ΔT
• How Do I Calculate How Much Plasterboard I Need for Walls and Ceilings?
  Plasterboard quantity calculator: 60 boards/m² standard, waste factors 10–20%, mortar/jointing compound coverage tables
• How Do I Calculate Pipe Flow Rates, Velocity & Pressure Drop for Domestic Plumbing?
  Pipe flow rate calculator: BS EN 806-3 loading unit method, velocity limits (1–3 m/s copper), pressure drop calculation
• How Do I Calculate Staircase Rise, Going, Headroom & Number of Treads?
  Staircase calculator: 220mm max rise, 220mm min going, 2000mm headroom, comfort formula 2R+G = 550–700mm per Approved Document K
• How Do I Calculate U-Values for Walls, Floors & Roofs?
  U-value calculator: worked examples for cavity wall, loft, and ground floor; Approved Document L targets; BS EN ISO 6946 method
• How Many Bricks and Blocks Do I Need? Quantity Calculator with Mortar & Waste
  Brick and block quantity calculator: 60 bricks/m² half-brick wall, 10 blocks/m² blockwork, mortar coverage tables
• How Many Tiles Do I Need? Calculating Quantities with Waste Allowance
  Tile quantity calculator: waste percentages by pattern, worked examples, adhesive/grout coverage tables
• Loft Insulation Depth Calculator: Mineral Wool and Blown Fibre to Hit Part L U-Values
• Markup vs Margin for Tradespeople: How to Convert Between the Two and Price for Target Profit
  Markup = profit/cost, margin = profit/price; convert margin=markup/(1+markup), markup=margin/(1-margin); conversion table; why "20% markup" ≠ "20% margin"; worked pricing for target profit; complements pricing/markup articles
• Max Cable Run Length Calculator: Voltage Drop, Derating & BS 7671 Compliance
  Cable run length: BS 7671 voltage drop limits (3% lighting, 5% power), mV/A/m values for T&E cables, derating factors for thermal insulation (0.50), grouping, and temperature
• Maximum Demand Calculator: After-Diversity Totals for Domestic Properties
  Maximum demand calculator: ADMD with diversity factors from BS 7671 Appendix 1, worked examples including EV charger impact
• Mortar Quantity Calculator: Mix Ratios, Bags of Cement and Sand Coverage Tables
  Mortar quantity calculator: 0.016m³/m² half-brick walling (1:5 mix), 0.030m³/m² one-brick, 0.002–0.003m³/m² repointing, 7–8 bags cement per m³ at 1:5, BS EN 998-2 Designation M4
• Paint Coverage Calculator: Litres Needed by Wall Area & Coats
  Paint coverage calculator: 12–14 m²/L sealed emulsion, 6–8 m²/L new plaster, worked examples for bedroom re-paint, new plaster, exterior masonry, and woodwork
• Plaster Quantity Calculator: Bags Per Square Metre by Coat Thickness
  Plaster quantity calculator: bags per m² for Thistle Bonding (5m²/bag), MultiFinish (18m²/bag), sand/cement render worked examples
• Radiator BTU Calculator: Room Size, Windows, Insulation & Exposure
  Radiator BTU/W calculator: heat loss factors 40–130 W/m² by insulation level, ΔT50 output correction for heat pumps, K1/K2/K3 output table, worked sizing examples
• Roof Tile Calculator: Tiles Per Square Metre by Profile, Plus Waste, Ridge and Valley
• Room Heat Loss Calculator: Detailed Method Using U-Values, CIBSE Guide A and Worked Examples
  Room heat loss calculator: fabric (U×A×ΔT) plus ventilation (0.33×N×V×ΔT) with worked example; design temperatures; heat pump vs gas radiator sizing comparison
• Room Heat Loss Calculator: W/m² Method, Worked Examples & Radiator Sizing
  Heat loss calculator: simplified W/m³ method (25–100 W/m³), element-by-element U-value×area×ΔT method, design temperatures, radiator ΔT50 ratings, heat pump correction factors
• Room Volume Calculator: Air Change Rates, MVHR Sizing and Ventilation Worked Examples
  Room volume calculator: L×W×H formula, Part F 2021 (0.3 l/s/m² floor area background ventilation), MVHR sizing worked example (3-bed, 50 l/s), commissioning tolerance ±10%, ACH to l/s conversion
• Screed Depth Calculator: Sand/Cement vs Liquid Screeds, Drying Times and Moisture Testing
  Screed depth calculator: 65–75mm sand/cement floating, 30mm anhydrite minimum, 30mm cover above UFH pipe crown, BS 8204 standard, drying rate 1mm/day, ≤75% RH hygrometer threshold before flooring
• Soakaway Sizing Calculator: BRE Digest 365 Percolation Test Method, Volume Calculation Formula and Worked Examples
  BRE Digest 365 percolation test Vp calculation, As = Vp × D × r × A / 2 formula, worked example for 80m² roof catchment in sandy loam, crate vs rubble comparison
• Three-Phase Voltage Drop Calculator: BS 7671 Method, Balanced and Unbalanced Loads, Worked Examples
  Three-phase voltage drop: BS 7671 mV/A/m method, balanced and unbalanced loads, power factor correction, worked motor supply example, cascaded circuit voltage drop budgeting
• Timber Joist Calculator: Span Tables, Spacing & Load Requirements
  Timber joist calculator: C16/C24 span tables at 400/450/600mm centres, notching and drilling rules, strutting requirements, worked examples for extension floor and loft conversion
• U-Value Calculation Guide: Thermal Resistance Method, Part L Targets and Wall, Roof and Floor Build-Ups
  Thermal resistance method R=d/λ, U=1/ΣR; Rsi 0.13 / Rse 0.04 (ISO 6946:2017); Part L1A 2021 limits wall 0.18/roof 0.11/floor 0.13; λ table; three worked build-ups; BR 443 (BRE) bridging; cross-refs insulation articles