Calculators

74 articles

• Battery Storage Sizing Calculator
  Sizes home battery storage from evening/overnight demand minus daytime solar offset, divided by round-trip efficiency (90-95% for LFP), with a worked kWh example.
• Boiler Flow Temperature Weather Compensation Calculator
  Weather compensation curve maths: Flow = room setpoint + slope × (room − outside); solving slope from index radiator design flow and design outdoor temp (−2 to −4°C lowland England); worked example 55°C/21°C/−3°C gives slope 1.42; Boiler Plus and ADL 2021 55°C design flow
• Boiler Flue Terminal Clearance Calculator
  Boiler flue terminal clearance calculator against BS 5440-1 minimum distances from openings, boundaries, gutters and other terminals, with worked positioning examples.
• Brick & Block Calculator: How Many Per m² UK + Mortar
  Brick and block quantity calculator: 60 bricks/m² half-brick wall, 10 blocks/m² blockwork, mortar coverage tables
• Brickwork Calculator: Bricks per M2 & Mortar Mix UK
• 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: BS 7671 Compliance Check
  Cable voltage drop calculator: BS 7671 mV/A/m values, 3%/5% limits, worked examples for ring final, shower, cooker circuits
• Circuit Breaker Sizing Calculator
  Circuit breaker (MCB) sizing calculator explaining the Ib ≤ In ≤ Iz rule with worked examples for immersion heater, ring final and EV charger circuits.
• CIS Deduction Calculator
  CIS deduction calculator: 20% verified/30% unverified/0% gross-status rates applied to labour-only (never materials/VAT), with HMRC verification steps and worked examples.
• Concrete Mix Ratios UK: C20, C25, C30 & Foundation Guide
• 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
• Consumer Unit Ways Calculator
  Consumer unit ways calculator: one way per final circuit plus BS 7671 Reg 132.8 minimum 2 spare ways, with a worked circuit-count example.
• Damp Proof Course Height Calculator
  DPC brick-course calculator: minimum 150mm above finished ground level per Approved Document C Clause C2, converted to standard UK brick coursing with worked examples.
• Day Rate to Hourly Rate Calculator
  Converts a day rate to a true hourly rate using realistic billable hours (6.5-7hrs, not 8) after admin/travel/setup, with a worked example.
• Day Work vs Fixed Price Calculator
  Decision calculator for day work vs fixed price based on scope-certainty variance, with a probability-weighted worked example showing how a flat risk premium can still underprice high-uncertainty jobs.
• Decking Board Calculator: How Many Boards Do I Need
  Decking board calculator: rows = deck width ÷ (board width + gap), lengths = run length ÷ board length, 10-20% waste by layout complexity; worked examples for rectangular, jointed, and diagonal layouts; standard board sizes and gap tables
• Decking Joist Spacing Calculator
  Decking joist spacing calculator: 27-28mm boards need 400mm max centres, 32mm+ boards up to 600mm, composite typically 300-400mm; C16/C24 joist span worked example
• Drainage Pipe Sizing Calculator: BS EN 752 Flow & Gradient
• Driveway Sub-Base Depth Calculator
  Sub-base depth calculator by use case: 100mm path/patio, 150mm domestic driveway, 200mm+ HGV/shared access, MOT Type 1 vs permeable SuDS options, with worked tonnage examples.
• EV Charger Cable Sizing Calculator
  EV charger cable sizing (6mm²/10mm² for 7kW), BS 7671 voltage-drop formula worked example, PME earthing check kept separate from Vd check
• EV Charger Diversity and Load Calculator
  Calculator showing a single EV charger gets zero BS 7671 diversity discount (100% of 32A), with worked ADMD examples and multi-charger DLM/DNO-managed load allocation for shared supplies.
• External Render Calculator: Coverage per Bag & Mix Ratios
• Fence Panel and Post Quantity Calculator
  Fence panel/post/gravel-board quantity calculator: panels = run length ÷ 1.85m spacing, posts = panels+1, worked example for a 24m run
• Fence Post Depth Calculator: UK Rules & Sizing Guide
  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 Calculator: Tonnes per M² by Depth & 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
• Guttering & Downpipe Sizing Calculator for Complex Roofs
• Guttering Fall and Gradient Calculator
  Guttering fall and gradient calculator explaining the 1:600 minimum vs 1:200 self-cleaning fall under BS EN 12056-3, with a worked 9.6m end-outlet run example.
• Guttering Quantity Calculator
  Materials-quantity takeoff calculator for guttering (lengths, unions, brackets, downpipes) with worked examples for a semi-detached house and bungalow
• Heat Pump Radiator Sizing Calculator: Delta-T & MCS Guide
  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 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 Do I Calculate VAT Under the Flat Rate Scheme for Construction?
  VAT Flat Rate Scheme calculator: fixed percentage applied to gross turnover rather than input/output VAT difference, with a worked construction-sector example.
• How Many Tiles Do I Need? Calculator & Waste Allowance
  Tile quantity calculator: waste percentages by pattern, worked examples, adhesive/grout coverage tables
• How Much Plasterboard Do I Need? Calculator & Sizing Guide
  Plasterboard quantity calculator: 60 boards/m² standard, waste factors 10–20%, mortar/jointing compound coverage tables
• Insulation Condensation Risk Calculator
  Glaser method interstitial condensation check to BS EN ISO 13788:2012 and BS 5250:2021: interface temperatures from thermal resistances, saturation vs actual vapour pressure using sd values; worked solid-wall IWI example (1,335 Pa vs 750 Pa, cleared by VCL sd ≥ 7m); fRsi ≥ 0.75 surface criterion
• Joist Span Calculator: Worked Examples by Timber Grade
  Joist span calculator: Approved Document A / Eurocode 5 basis, three worked examples by timber grade (C16/C24), notes inter-source table variance as a verify-before-use caveat
• Kitchen Worktop Quantity Calculator
  Worked worktop quantity calculator from linear run length × standard 600mm depth, covering corner returns, waste allowance, and stone/laminate/timber material differences.
• Loft Conversion Headroom Calculator
  Calculates final clear loft headroom from ridge/rafter height minus floor build-up (~75mm) and insulation intrusion, with Building Regs minimum headroom thresholds and worked examples.
• Loft Insulation Depth Calculator: Part L U-Values UK
• Markup vs Margin Calculator: Convert & Price for Profit UK
  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: BS 7671 Voltage Drop Calculator
  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: ADMD for Domestic Properties
  Maximum demand calculator: ADMD with diversity factors from BS 7671 Appendix 1, worked examples including EV charger impact
• Mortar Calculator: Mix Ratios & Coverage Guide BS 5628
  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 per m² & Coats Guide
  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
• Paving Slab Quantity Calculator
  Slab quantity calculator by area/format with wastage %, sub-base and mortar bed volumes, worked examples for concrete flags and natural stone packs
• Pipe Flow Rate Calculator: Velocity & Pressure Drop Guide
  Pipe flow rate calculator: BS EN 806-3 loading unit method, velocity limits (1–3 m/s copper), pressure drop calculation
• Plaster Calculator: Bags Per m² & Coat Thickness Guide
  Plaster quantity calculator: bags per m² for Thistle Bonding (5m²/bag), MultiFinish (18m²/bag), sand/cement render worked examples
• R-Value Calculator: Working Out Insulation Thermal Resistance
  R-value calculator: series-addition method for build-up thermal resistance, three worked examples (loft top-up, product substitution, cost-per-R comparison), companion to the existing U-value calculator
• Radiator BTU Calculator: Room Heat Loss & Sizing Guide
  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
• Rafter Length Calculator: Pitch, Run and Common Rafters
  Common rafter length = √(run² + rise²) = run × sec(pitch); worked examples (3m run @30° = 3.46m) + pitch reference table; eaves overhang, birdsmouth; Approved Document A, BS 5534, BS 5268/Eurocode 5, BS 8103
• Render Quantity Calculator: How Much Render Do I Need?
  Step-by-step render quantity takeoff with worked examples for sand-cement, monocouche, silicone and lime systems
• Roof Pitch Calculator: Degrees, Ratio and Percentage
  Converts roof pitch between degrees, ratio and percentage with worked examples and minimum-pitch-by-material table
• Roof Tile Calculator: Tiles Per m² & Waste Allowance UK
• Roof Tile Quantity Calculator
  Roof tile quantity calculator — sloped-area method, gauge/cover-width formulas for single- vs double-lap tiles, ridge/verge/hip run-length calcs, with a fully worked example
• Roof Truss Spacing Calculator
  Indicative truss-count and batten take-off calculator for pricing/ordering (400mm/600mm centres), explicit that actual truss spacing is engineer-designed per project, not DIY span-tabled.
• Room Heat Loss Calculator: U-Values & CIBSE Guide A
  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/m³ Method & 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: MVHR Sizing & Air Change Rates UK
  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
• Scaffold Tower Load Calculator
  Mobile tower load checks to BS EN 1004-1:2020 class 3 (2.0 kN/m²): platform SWL vs workers (100 kg each) plus materials, leg load = (self-weight + imposed) ÷ 4 × 1.5 against castor rating and ground bearing; Work at Height Regulations 2005 Schedule 3 and 7-day inspections
• Screed Depth Calculator: Min Depths & Drying Times UK
  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
• Screed Quantity Calculator: Ordering Bags, Ready-Mix and Liquid Screed
• Skip Size Selector: Choosing the Right Skip for the Job
  UK skips sized in cubic yards: 2-yard mini → 8-yard builders (most common) → RoRo 20–40 yard; bin-bag/weight equivalents; skip on highway needs council permit (Highways Act 1980 s139) + lights/markings; EPA 1990 s34 duty of care
• Skirting Board Quantity Calculator: How Much Do I Need
  Calculator for skirting board linear metreage and stock-board count from room perimeter, door deductions, and complexity-based waste allowances
• Soakaway Sizing Calculator: BRE 365 Percolation Method
  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
• Staircase Rise & Going Calculator: BS 5395 & Part K Rules
  Staircase calculator: 220mm max rise, 220mm min going, 2000mm headroom, comfort formula 2R+G = 550–700mm per Approved Document K
• Three-Phase Voltage Drop Calculator: BS 7671 Method
  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
• Tile Adhesive Coverage Calculator
  Tile adhesive coverage calculator relating trowel notch size and bed depth to bags-per-m², with worked bathroom and large-format kitchen examples.
• Timber Joist Span Tables UK: Spacing & Load Calculator
  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 Calculator: Part L Targets & Thermal Resistance
  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
• Underfloor Heating Pipe Spacing Calculator
  Worked pipe-spacing calculator (100-300mm centres vs MWT vs W/m² output) for sizing wet UFH loops from room heat loss, with pipe-quantity and loop-count worked examples.
• Van Running Cost Calculator
  Van running cost calculator: full cost-per-mile worked example (finance/depreciation usually exceeds fuel), HMRC AMAP 55p/25p rate from April 2026, AMAP-vs-actual-cost self-employed election.
• Wallpaper Roll Calculator: How Many Rolls Does a Room Need
  Wallpaper roll calculator using drop-based method (not area-based) for standard 10.05m × 0.53m UK rolls; straight/drop/random pattern-match wastage rules; three worked examples (bedroom, feature wall, stairwell)
• What Cable Size for an Electric Shower? Circuit Calculator
  Electric shower cable sizing (6mm²/10mm² by kW), design current, installation method and BS 7671 voltage-drop check worked examples
• What Size Boiler Do I Need? kW Sizing Calculator
  Boiler kW sizing: combi via flow-rate formula (kW = l/min÷60 × ΔT × 4.18), system/regular via BS EN 12831-1 heat loss; worked examples