Our calculation methodology

Three kinds of calculation

Physics-based calculations use established relationships such as energy = power × time. Guideline-based estimates adapt published sizing guidance. Empirical estimates use practical assumptions and should be treated as a starting range. We label these differences on every tool.

Electrical energy

E (kWh) = P (W) ÷ 1,000 × t (hours). Rated power is not always average power: thermostats, compressors and variable-speed motors cycle. Use measured energy or an energy label where available.

Electricity cost

Cost = energy (kWh) × price per kWh. Enter a tariff in the selected currency; changing the currency changes its label, not the numeric tariff or exchange rate. Currency, language and measurement units are independent.

The general cost tool repeats the selected monthly schedule over 12 months. Weekly cycle tools use 52 weeks per year and divide annual cost by 12 for a monthly average. Fixed charges are excluded.

Water heating

Q = m × c × ΔT, using water density approximately 1 kg/L and specific heat c = 4.186 kJ/(kg·°C). Heating time t = Q ÷ (P × η), with power in kJ/s. Electrical energy equals thermal energy divided by efficiency.

Efficiency is an estimated input, not a measured promise. The model excludes phase changes, ongoing heat loss after heating, tank recovery behavior and altitude effects on boiling point. Target temperature must not be below starting temperature.

Microwave power conversion

P₁ × t₁ ≈ P₂ × t₂. A 1,000 W instruction for 3 minutes becomes approximately 4 minutes 17 seconds at 700 W. Use cooking output wattage, not electrical input power.

This is an energy-equivalence estimate. Food geometry, moisture, containers and microwave distribution affect results. Stir, allow standing time and verify safe internal temperature.

Clean air delivery rate (CADR)

Volume = length × width × height. CADR (m³/h) = volume (m³) × ACH. CADR (CFM) = volume (ft³) × ACH ÷ 60.

Room volume (m³) = CADR (m³/h) ÷ ACH. Floor area (m²) = volume ÷ ceiling height (m).

Equivalent air changes (ACH)

ACH = CADR (m³/h) ÷ volume (m³), or ACH = CADR (CFM) × 60 ÷ volume (ft³).

One CFM equals 1.69901079552 m³/h. CADR refers to particle removal; it is not outdoor-air ventilation. The model assumes ideal mixing, one open room and operation at the rated fan setting. Select ACH for your circumstances; no single value guarantees health protection.

Oven to air fryer conversion

Conventional oven recipes start at 80% of the original time and 20°C (36°F) lower. Convection/fan recipes keep their original time and temperature before optional food adjustments, avoiding a second convection adjustment. These are empirical assumptions, not guaranteed cooking instructions. Both unit systems use one Celsius-based calculation; switching units does not change the recommendation.

Room air-conditioner sizing

Start with the ENERGY STAR floor-area table. Scale ceiling height relative to 8 ft, apply sun factors of 0.9/1/1.1, and add 600 BTU/h per occupant beyond two. Insulation factors of 0.85/1/1.2 are our own empirical adjustments, not ENERGY STAR coefficients. BTU/h ÷ 3,412.14 = kW of cooling.

This calculator provides a room air-conditioner sizing estimate and does not replace a professional HVAC load calculation.

Space heater sizing

Estimated watts = room volume (m³) × temperature rise (°C) × assumed loss coefficient. Coefficients of 0.8, 1.2 and 1.8 W/(m³·°C) represent good, average and poor insulation. These are site-selected empirical assumptions; the displayed range is ±20%. Energy (kWh) = watts ÷ 1,000 × hours.

Outdoor conditions, drafts and external wall area can dominate heat loss.

Water heater sizing

Assumed peak demand = showers × minutes × 8 L/min × 0.7 hot-water fraction + 6 L per dishwasher use + 20 L per laundry use + 5 L per occupant. Tank range = 0.8–1.2 × estimated demand. All these allowances are site-selected empirical assumptions; this does not calculate a certified first-hour rating.

Tank volume is not a first-hour delivery rating. Recovery, incoming temperature and simultaneous demand need separate verification before purchase.

Dehumidifier sizing

Capacity is selected from ENERGY STAR area-and-dampness guidance, not derived from a humidity mass-balance equation. Liters/day = US pints/day × 0.473176.

A cold basement can reduce moisture removal relative to laboratory ratings.

Units, precision and review

1 foot = 0.3048 meters; 1 US gallon = 3.785411784 liters; °F = °C × 9/5 + 32; 1 kW ≈ 3,412.14 BTU/h. Gallons throughout this site mean US liquid gallons, not UK imperial gallons. Language and unit system are separate controls.

Display rounding matches the method: approximate cooking and sizing use ranges, while energy and dimensional calculations retain useful numerical detail. References support the stated relationship or context; a reference does not endorse every estimated parameter. All languages share one calculation engine.