Electrical preliminary sizing
Use engineering design calculators to estimate cable sizing, voltage drop, conduit fill, and load assumptions before moving into code review or procurement.
Engineering Topic Hub
Engineering Design Calculators
Engineering calculators for electrical sizing, voltage drop, conduit fill, HVAC duct sizing, BTU estimates, and pipe or tank volume.
This subhub groups engineering tools that affect design assumptions and field planning. Treat outputs as preliminary estimates, then confirm safety-critical work against codes, manufacturer data, and qualified review.
Quick answer
Use this hub for preliminary engineering design math: electrical sizing, voltage drop, conduit fill, HVAC duct sizing, BTU estimates, and pipe or tank volumes. These tools are for planning and checking assumptions, not for replacing code review, manufacturer data, stamped design work, or field verification.
Priority Tool
BTU Calculator
Estimate room heating and cooling BTU/hr, cooling tons, and kW from room size, climate, insulation, sun, occupants, and internal gains.
Open toolPriority Tool
Conduit and Wire Fill Calculator
Estimate conduit fill percentage, minimum conduit size, and educational derating implications for raceway planning.
Open toolPriority Tool
Duct Size / Ductulator and CFM Calculator
Estimate HVAC duct dimensions, velocity, pressure-drop behavior, and round/rectangular equivalents using digital ductulator assumptions.
Open toolPriority Tool
Electrical Cable/Wire Size and Voltage Drop Calculator
Estimate cable size, AWG/mm2 conversion, voltage drop, and basic ampacity checks for AC/DC scenarios.
Open toolPriority Tool
Ohm's Law Calculator
Solve voltage, current, resistance, and power from any two known electrical circuit values, with runtime energy and cost estimates.
Open toolPriority Tool
Pipe / Tank Volume and Dimensions Calculator
Calculate tank, pipe, and pool capacity with partial-fill estimates, missing-dimension solving, and metric/imperial conversion outputs.
Open toolStart With The Specific Task
Choose the calculator that matches the real decision: estimate, compare, convert, plan, or verify.
Keep Assumptions Visible
Record rates, units, dates, policy limits, and user-provided inputs before acting on a result.
Use The Parent Hub For Breadth
Return to Engineering Calculators when the problem crosses into a neighboring topic.
How To Use This Hub Well
These hub pages group calculators by decision type. Use the table below as a quality check before acting on any single output.
| Review area | What to do |
|---|---|
| Units first | Convert units and dimensions before calculating so voltage, length, flow, area, volume, and pressure assumptions are consistent. |
| Design assumption log | Record material, environment, load case, safety factor, code edition, and manufacturer constraints beside the result. |
| Independent check | Use calculator output as a first pass, then verify safety-critical decisions against applicable standards and qualified review. |
Worked Examples
| Scenario | How to use the calculators |
|---|---|
| Voltage drop screen | Estimate drop from conductor size, material, load, length, and phase before checking final design against applicable electrical requirements. |
| Duct sizing screen | Use airflow and velocity assumptions to compare possible duct dimensions before detailed pressure-loss design. |
| Tank volume check | Convert drawing dimensions into volume to catch order-of-magnitude mistakes before procurement. |
When To Use Engineering Calculators
HVAC and building estimates
Use duct, BTU, and airflow-related tools to frame early design options, compare assumptions, and communicate sizing ranges before final design review.
Pipe, tank, and volume planning
Use volume and dimension calculators to check container, pipe, or tank assumptions before ordering materials or converting drawings into quantities.
Suggested Engineering Workflow
Step 1
Confirm units, material assumptions, environment, load case, and safety margin before entering values.
Step 2
Use calculator output for preliminary planning, not as the final authority for safety-critical design.
Step 3
Cross-check results against applicable electrical, mechanical, plumbing, HVAC, manufacturer, and local code requirements.
Step 4
Document assumptions so another reviewer can reproduce the estimate and identify what must be verified in the field.
Limits And Safety Checks
| Limit | What it means |
|---|---|
| Not code approval | Calculator output does not establish compliance with NEC, mechanical, plumbing, building, fire, or local code requirements. |
| Manufacturer data matters | Equipment ratings, derating, installation conditions, and material properties can change the final design. |
| Field conditions vary | Bends, fittings, ambient temperature, routing, pressure losses, and tolerances can move real-world results. |
Sources Reviewed
| Source | URL | Why it is relevant |
|---|---|---|
| NIST SI units | https://www.nist.gov/pml/owm/metric-si/si-units | Reviewed June 2026 for unit and measurement context. |
| NIST writing with SI units | https://www.nist.gov/pml/owm/writing-si-metric-system-units | Reviewed June 2026 for unit-format guidance. |
| ASHRAE duct design resources | https://www.ashrae.org/advertising/handbook-advertising/fundamentals/duct-design | Reviewed June 2026 for duct-design reference context. |
| ASHRAE duct fitting database | https://www.ashrae.org/technical-resources/bookstore/duct-fitting-database | Reviewed June 2026 for duct-fitting resistance reference context. |
Related Engineering Resources
Electrical Cable Wire Size Calculator
Estimate wire size and voltage drop assumptions before electrical design review.
Conduit Wire Fill Calculator
Check conduit fill planning against conductor and raceway assumptions.
Duct Size Calculator
Estimate duct dimensions from airflow, velocity, and friction assumptions.
Engineering Calculations Guide
Read the supporting guide for assumptions, verification limits, and safe use.
Frequently Asked Questions
No. Use them for preliminary estimates and assumption checks. Safety-critical work still needs applicable code review, manufacturer data, qualified engineering judgment, and field verification.
Record units, material, load case, environment, code edition, safety factor, manufacturer constraints, and the date of the estimate so another reviewer can reproduce the result.
Differences usually come from units, assumptions, derating, material properties, friction or loss models, rounding, and whether the calculator is screening or designing.