All calculators
57 calculators in six categories. Each one shows its formula, assumptions and a worked example.
Home Projects
Concrete
- Concrete Bag CalculatorConvert a known concrete volume into 40, 50, 60 and 80 lb bags.
- Concrete Footing CalculatorConcrete for continuous (strip) footings and curbs by linear foot.
- Concrete Post Hole & Column CalculatorConcrete bags for fence post holes, deck piers and round columns (sonotubes).
- Concrete Slab CalculatorCubic yards, bags and cost for slabs, patios, driveways, sidewalks and pads.
- Concrete Steps CalculatorConcrete volume for a solid set of poured steps with an optional top landing.
Deck
- Deck Board CalculatorDeck boards, linear feet and deck screws for a rectangular deck.
- Deck Footing & Post CalculatorNumber of deck posts and footings, and concrete for round footings.
- Deck Joist CalculatorNumber of joists, joist hangers and rim board length for a deck frame.
- Deck Railing & Baluster CalculatorRailing posts and balusters with the 4-inch sphere rule.
- Stair & Stringer CalculatorRisers, riser height, treads, total run and stringer length from total rise.
Fence
Roofing
Flooring
Insulation
Home Energy
HVAC
- BTU to kW & Tons ConverterConvert heating and cooling capacity between BTU/h, watts, kW and tons.
- CFM & Air Changes per Hour CalculatorConvert between room airflow (CFM) and air changes per hour (ACH).
- Duct Size Calculator (Velocity Method)Round duct diameter and rectangular duct size for an airflow and target velocity.
- Heating Load & Furnace Size EstimateDesign heating load from walls, windows, ceiling and air leakage; furnace input size from AFUE.
- AC BTU Calculator (Room Cooling)Room air conditioner or mini-split size in BTU/h using the ENERGY STAR room sizing method.
Energy bills
Solar
- Solar Battery Size CalculatorBattery capacity (kWh) for backup days, depth of discharge and efficiency.
- Solar Payback & Savings CalculatorNet cost, payback year and lifetime savings for a solar system with your own rates and incentives.
- Solar Panel & System Size CalculatorSolar system size (kW), number of panels, roof area and estimated yearly production.
Plumbing
Pipe flow
- Pipe Flow & Water Velocity CalculatorWater velocity from flow rate and pipe size, or flow rate from velocity.
- Water Pipe Size Calculator (Velocity Method)Smallest copper, PEX or PVC pipe that keeps water velocity under a limit.
- Pipe Volume CalculatorGallons of water held in a length of pipe, and its weight.
- Pipe Pressure Drop Calculator (Hazen-Williams)Friction pressure loss in a water pipe plus elevation change.
Electrical
Power
Wiring
- Extension Cord Voltage Drop CalculatorVoltage at the tool for an extension cord gauge, length and load.
- Voltage Drop CalculatorVoltage drop and percent drop for copper or aluminum conductors by AWG size and length.
- Wire Size Calculator (Voltage Drop)Smallest conductor that keeps voltage drop under your limit.