Engineering
Bolt Torque
Bolt Torque applies a standard engineering formula in simplified form.
What this does
Bolt Torque applies a standard engineering formula in simplified form.
Engineering calculators are simplified versions of the equations professionals use, and they are honest about being simplifications. Ohm's law relates voltage, current, and resistance in one tidy triangle: voltage equals current times resistance, and knowing any two gives you the third. Beam calculations relate a load to how much a beam bends and how much stress its material feels. HVAC math relates a room's heat gains and losses to the equipment size that can handle them. Each one turns a physical law into a number you can act on.
The formula, explained plainly
Ohm's law is the entry point to all electrical math. Voltage (volts) is the push, current (amps) is the flow, resistance (ohms) is the opposition, and V = I x R ties them together. Power adds the second equation: watts equal volts times amps. Together they answer practical questions like what fuse a circuit needs, whether a wire gauge is safe for a load, and how much heat a resistor will dump into an enclosure. The law assumes steady DC or simple resistive AC loads; motors and electronics with reactive behavior need more advanced treatment.
Beam basics come down to two questions: will it break, and will it sag too much. Bending stress depends on the load, the span, and the beam's cross-section shape, captured in the section modulus. Deflection depends on the same inputs plus the material's stiffness (Young's modulus) and the moment of inertia. A beam can be strong enough yet still feel bouncy underfoot, which is why deflection limits (often span divided by 360 for floors) matter as much as strength in real design.
HVAC sizing is heat accounting. Every room gains heat through walls, windows, roofs, people, lights, and equipment, and loses heat the same ways in winter. The Manual J method (the industry standard for homes) adds up all these gains and losses to find the required heating and cooling capacity, usually in BTU per hour or tons (one ton equals 12,000 BTU per hour). The classic mistake is oversizing: a too-big air conditioner cools the air so fast it never runs long enough to dehumidify, leaving the house cold and clammy.
Unit consistency is the unglamorous skill behind every engineering number. Mixing millimeters with meters, or BTU with watts, is the most common source of wrong answers, more common than misunderstanding the physics. Good practice is to convert all inputs to one coherent system before calculating, then convert the answer to whatever unit you need. The calculator does this bookkeeping for you, but checking that inputs are in the stated units is still your job.
How to use it
- Enter force (n).
- Enter radius (m).
- Read the instant result and the breakdown below it.
- Adjust any input to compare scenarios.
Worked example
With force (n) = 100, radius (m) = 0.5, the result is 50 Nm. Defaults are typical textbook values for the equation.
Common mistakes
- Using Ohm's law on AC motor or transformer circuits as if they were simple resistors, ignoring reactance and power factor, which understates real current.
- Sizing wire by the load's normal current without checking the breaker rating, when the wire must safely carry whatever the protective device allows.
- Checking a beam's strength but not its deflection, ending with a floor that holds the load fine yet bounces annoyingly under footsteps.
- Forgetting that a beam's capacity drops with the square of the span: doubling the span quarters the load it can carry, a relationship intuition badly underestimates.
- Oversizing HVAC equipment 'for safety,' which short-cycles the system, ruins humidity control, and actually costs more to run than a correctly sized unit.
- Using rule-of-thumb tons-per-square-foot for HVAC sizing in a well-insulated or leaky house, when the rule was calibrated for average construction decades ago.
- Mixing metric and imperial units mid-calculation, the classic engineering error that has destroyed real hardware, so verify every input's unit.
- Ignoring the beam's own weight (dead load) on long spans, where the beam itself becomes a significant part of the total load.
Limitations
- Safety factors are your responsibility: engineering practice applies margins (often 1.5x to 3x) that a raw calculator output does not include automatically.
- These are educational simplifications, not stamped engineering: real structural, electrical, and mechanical designs must be done or reviewed by a licensed professional and meet local codes.
- Ohm's law calculators assume resistive DC or simple AC loads; inductive and capacitive circuits, harmonics, and three-phase systems need proper analysis.
- Beam calculators cover standard simply-supported and cantilever cases with uniform or point loads; continuous beams, torsion, lateral buckling, and dynamic loads are outside their scope.
- HVAC estimates use simplified heat-transfer assumptions; a proper Manual J accounts for orientation, shading, infiltration rates, and duct losses in detail.
Expected accuracy
The underlying formulas (Ohm's law, beam bending equations, steady-state heat transfer) are exact within their assumptions, so the math is precise for the inputs given. Real-world accuracy depends on input quality: measured loads, actual material grades, and true insulation values. For anything structural, electrical, or load-bearing, treat calculator results as a starting estimate and have a licensed professional verify the design.
Privacy
Everything you type stays on your device. The calculation runs in your browser with JavaScript; no input is sent to a server, stored in an account, or shared with anyone.
Sources and standards
- Electrical math follows Ohm's law and standard power relationships; beam calculations use classical Euler-Bernoulli beam theory with standard deflection limits; HVAC sizing follows the heat-balance principles of ACCA Manual J (residential load calculation standard).
Bottom line
Bolt Torque puts real engineering equations within reach for planning, checking quotes, and learning. Respect the assumptions, keep your units consistent, and bring a licensed professional into the loop before anything gets built, wired, or installed.
Key insight
Reality has safety factors for a reason: materials vary, loads surprise, and installations are imperfect. Never design to the theoretical limit for anything that can hurt someone.
Frequently asked questions
What is deflection and why does it matter?
Deflection is how much a beam sags under load. Even a beam strong enough to be perfectly safe can sag enough to crack finishes or feel bouncy. Floors are commonly limited to span/360 deflection under live load, which is often the controlling requirement rather than strength.
How is HVAC size calculated for a house?
A proper load calculation (Manual J) sums heat gains and losses through every surface, window, and air leak, plus internal gains from people and appliances. The total, in BTU per hour, determines equipment size. Rules of thumb like square footage per ton are unreliable for anything but average construction.
What does a ton of air conditioning mean?
One ton of cooling equals 12,000 BTU per hour, a historical reference to melting a ton of ice per day. A 3-ton system moves 36,000 BTU per hour. The tonnage must match the home's calculated load; bigger is not better because oversized systems short-cycle and dehumidify poorly.
Why is oversized HVAC equipment bad?
An oversized air conditioner satisfies the thermostat quickly and shuts off before running long enough to wring moisture from the air. The result is a cold but clammy house, more on-off cycling wear, and higher energy bills. Correct sizing prioritizes long, steady run cycles.
How do I convert BTU to watts?
One watt equals about 3.412 BTU per hour, so divide BTU/h by 3.412 to get watts. A 12,000 BTU/h (one ton) air conditioner moves about 3,517 watts of heat. Note this is heat moved, not electricity consumed; the electrical draw is much lower thanks to the refrigeration cycle's efficiency.
What is the difference between series and parallel resistance?
In series, resistances add directly (R total = R1 + R2) and the same current flows through each. In parallel, the total is less than the smallest resistor: 1/R total = 1/R1 + 1/R2, and voltage is the same across each branch. Most house wiring is parallel, which is why one bulb burning out does not kill the rest.
How do I calculate the load on a floor joist?
Add the dead load (structure, flooring, typically 10 to 15 psf) and live load (people, furniture; 40 psf is standard for living areas), multiply by the joist spacing to get load per linear foot, then check bending and deflection over the span. Code tables exist for common lumber sizes and spans.
What is a safety factor in engineering?
A safety factor is the margin between a component's rated capacity and the expected load, accounting for unknowns in materials, loads, and workmanship. Structural design commonly uses factors around 1.5 to 3 depending on the code and consequence of failure. Calculator outputs are unfactored, so apply appropriate margins.
How do I estimate heat loss through a wall?
Heat loss equals the wall area times the temperature difference divided by the wall's R-value (or times its U-value). A 20 square meter wall at R-13 with a 20 degree C difference loses about 307 watts. Summing this over all surfaces is the core of a heating load calculation.
Can I use these calculators for a real building project?
Use them for learning, rough planning, and checking that a quote is in a sane range. Do not use them as the basis for actual construction, wiring, or equipment installation without review by a licensed engineer or qualified contractor, since codes, safety factors, and site conditions all require professional judgment.
What is Ohm's law in simple terms?
Voltage equals current times resistance (V = I x R). It means that for a fixed resistance, doubling the voltage doubles the current. Rearranged, it also gives current from voltage and resistance (I = V/R) or resistance from voltage and current (R = V/I). It is the single most used equation in electrical work.
How do I calculate electrical power?
Power in watts equals voltage times current (P = V x I). A 12-volt device drawing 2 amps uses 24 watts. Combined with Ohm's law, you can also compute power from any two of the three quantities, for example P = I squared x R when you know current and resistance.
What size wire do I need for a circuit?
Wire size depends on current, length (voltage drop over distance), and installation conditions. As a rough guide, 14 AWG suits 15-amp circuits and 12 AWG suits 20-amp circuits in typical home wiring, but long runs need upsizing for voltage drop. Always follow your local electrical code and have an electrician verify.