Calculators
Every calculator, and the standard behind it
That count is the calculators available on a paid plan. It excludes unreleased calculators still in testing, and superseded pages kept reachable so existing saved sheets still open.
Electrical
Distribution design to BS 7671 and the IET On-Site Guide, plus the plant that hangs off it.
Circuit Design
Sizes the cable, checks the adiabatic condition, selects the protective device and verifies earth-fault loop impedance in one pass.
BS 7671
Voltage Drop
Volt drop along a circuit from the tabulated mV/A/m figures, with the reactive term where it matters.
BS 7671 Appendix 4
Fault Level
Prospective fault current at a point in the installation, single- and three-phase.
BS 7671 Appendix 14
Load Schedule
Connected load and maximum demand for an installation, applying the tabulated diversity factors.
IET On-Site Guide Table A2
DB Schedule
Builds a distribution board schedule circuit by circuit from the load schedule.
BS 7671 Reg 536.4.202 / BS EN IEC 61439-1
Motor Starter
Contactor and overload selection for direct-on-line and star-delta starting.
BS EN IEC 60947-4-1:2019 / BS 7671
Power Factor Correction
Capacitor bank size to reach a target power factor, with the resulting kVA saving.
BS 7671 / CTG007
Generator
Generator set sizing including step-load acceptance and the resulting voltage and frequency dip.
ISO 8528-1 / -5
UPS
UPS rating and autonomy from the connected load and the required runtime.
IEC 62040-3:2021
Lighting Design
Luminaire count by the lumen method for a target maintained illuminance.
BS EN 12464-1:2021
Emergency Lighting
Escape-route, open-area and high-risk illuminance, points of emphasis and duration for an emergency scheme.
BS 5266-1:2025 / BS EN 1838:2024
EV Charging
Charge-point maximum demand, current per phase, the DNO connection route and the G98/G99 route for V2G points.
BS 7671 Section 722
AC & Refrigeration
Cooling and heating loads by the CIBSE or ASHRAE method, and the refrigeration plant that serves them.
Space Load
Room heating and cooling loads, by the cyclic admittance method or the radiant time series.
CIBSE Guide A / ASHRAE Fundamentals
Solar Gain
Solar heat gain through glazing for a given station, orientation and shading.
CIBSE Guide A
Refrigeration Loads
Cold-store load build-up: transmission, infiltration, product, and internal gains.
IOR Cold Store CoP 2020 / ASHRAE
Refrigerant Pipe Sizing
Suction, liquid and discharge lines for one circuit, by pressure loss or by velocity, with riser oil return, liquid lift and pipework charge.
ASHRAE Refrigeration 2022 / Danfoss
Condensate Drain
Condensate flow and drain size for cooling coils, with trap depth.
CIBSE Guide G / AD H / BS EN 12056-2
Machinery Room
Machinery-room ventilation and leak detection for a refrigerant charge.
BS EN 378-3
Ventilation
Air rates, duct sizes and the pressure and noise that follow from them.
Ventilation Design
Supply and extract rates for a space, by occupancy, area or air-change basis.
CIBSE Guide A / AD F / BB101 / HTM 03-01 / BS EN 16798-1
Whole Dwelling
Whole-dwelling and room extract rates for a residential scheme.
Approved Document F Vol 1 (2026)
Natural Ventilation
Opening areas and achievable flow from wind and buoyancy.
BS EN 16798-7 / CIBSE Guide A / AD F
AHU Duty
Air-handling unit duty, coil loads and heat-recovery performance.
CIBSE Guide B3 / ASHRAE Fundamentals Ch.1 / AD L Vol 2
Standalone Fan
Fan duty and specific fan power against the Part L limit, or the fan energy index.
Approved Document L Vol 2 / CIBSE Guide B4 / AMCA 208
Duct Sizing
Duct sizes by constant pressure drop or velocity, circular, rectangular or flat-oval.
CIBSE Guide B2 / Guide C
Ductwork Pressure Loss
System pressure loss along an index run, straight lengths plus the fitting catalogue.
CIBSE Guide C
Duct Insulation
Insulation thickness for heat loss, condensation control or personnel protection.
BS 5422:2023
Grille
Neck and face velocity against the CIBSE B2 envelope, and throw, for a required flow.
CIBSE Guide B2
Louvre
Louvre free area and pressure drop for intake and discharge openings.
CIBSE Guide C
Duct Noise
Breakout and regenerated noise along a duct run, to a room NR level.
CIBSE Guide B4
Plumbing & Heating
Wet systems end to end: heat loss, heat source, distribution, storage and drainage.
Heat Loss
Room-by-room design heat loss for a dwelling, with each room's radiator sized for the flow temperature.
CIBSE Domestic Heating Design Guide 2026 / BS EN 12831-1:2017
Heat Source Sizing
Boiler or heat pump output for a commercial building or a single dwelling, with combi selection and a heat pump's yearly electricity estimate.
CIBSE Guide B1 / AM16 · CIBSE Domestic Heating Design Guide 2026 · MCS MIS 3005-D / MCS 031 a)
Heat Pump Noise
Sound level at each neighbour's window from an air source heat pump, against the 37 dB(A) permitted development limit.
MCS 020 a) Issue 1.1
Ground Loop Sizing
Length of borehole, horizontal or slinky ground loop for a ground source heat pump under 30 kW.
MCS MIS 3005-D / MGD 007
Underfloor Heating
Floor output and pipe spacing against the surface-temperature limits.
BS EN 1264-2:2021 / CIBSE Domestic Heating Design Guide 2026 / MCS MGD 007
Expansion Vessel
Vessel volume and fill pressure from system volume, temperature range and pressures.
BS EN 12828 Annex D and UK National Annex / CIBSE Domestic Heating Design Guide 2026
Hydronic Pipe Sizing
Heating and chilled pipe sizes by pressure drop, or by velocity for a house.
CIBSE Guide C / CIBSE Domestic Heating Design Guide 2026
Pipe Insulation
Insulation thickness for heat loss, freeze and condensation control.
BS 5422:2023 / CIBSE Domestic Heating Design Guide 2026
Cold Water Pipe Sizing
Cold water pipe size from the design flow, checked for velocity and for the pressure left at the outlet.
CIBSE Guide C / Guide G / BS EN 806-3
Hot Water Storage
Hot water storage for a commercial building's daily demand, or a dwelling's cylinder with its coil and reheat time.
CIBSE Guide G / CIBSE Domestic Heating Design Guide 2026 / MCS MIS 3005-D
Drainage
Discharge stack size from the appliances connected, and rainwater pipe size from the roof area.
BS EN 12056-2 and -3 / AD H
Renewables
Solar output by the MCS and SAP methods, with the connection thresholds.
Solar Thermal
The MCS 024 performance estimate and fuel saving, and the SAP monthly method, for solar hot water.
MCS 024:2025 / SAP 10.3 Appendix H / MCS MIS 3001
PV Sizing
The MCS 032 standard estimate and the SAP yield, self-consumption from the MCS tables, and inverter current against the G98 and G99 thresholds.
MCS 032:2025 / SAP 10.3 Appendix M / MCS MIS 3002
See the working before you trust it
For several of these we publish our own verification: fixed worked examples run through the same calculation code, compared line by line with the values printed in the standard, with every delta and pass or fail shown.
MEPCalc is in a closed tester phase ahead of public launch.