Five everyday calculators tools for electricians, DIYers, and engineers. Quick, practical, and U.S.-ready.
Quick chooser for Calculators
Not sure which one to start with? Use these rules of thumb:
- Long runs, EV chargers, outdoor circuits → Voltage Drop
- Convert between kW / kVA / HP / Amps → Power Converter
- Sizing UPS / RV / off-grid batteries → Battery Runtime
- Pick transformer size from load/voltage → Transformer kVA
- Estimate monthly bill / appliance cost → Energy Cost
U.S. presets included: 120/240 V split-phase, 120/208Y three-phase, 277/480Y three-phase, 60 Hz.
1) Voltage Drop Calculators
What it does. Estimates voltage drop (%) and end-of-run voltage by system voltage / phase / length / conductor / load current / PF. Includes common U.S. presets and 3% (branch) / 5% (feeder) targets.
Use it for.
- Long residential runs (shed, dock, detached garage).
- EVSE circuits, heat pumps, well pumps.
- Parking lot / site lighting, low-rise feeders.
Inputs. 120/240 split-phase, 120/208Y, 277/480Y; copper/aluminum; AWG or mm²; temperature and conduit correction (optional); PF if known.
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U.S. tips.
Verify ampacity/adjustments with the NEC and your AHJ (Authority Having Jurisdiction).
Many continuous loads use the 80% rule; EVSE often treated as continuous.
Treat this as planning math; pick the next larger gauge when borderline.
| AWG | mm² |
| 14 | 2.08 |
| 12 | 3.31 |
| 10 | 5.26 |
| 8 | 8.37 |
| 6 | 13.3 |
| 4 | 21.2 |
| 2 | 33.6 |
| 1/0 | 53.5 |
2) Single- / Three-Phase Power Converter
What it does. Converts among kW / kVA / HP / Amps across 1-phase and 3-phase systems; lets you set PF and voltage.
Common presets. 120/240 V split-phase (residential), 120/208Y V (light commercial), 277/480Y V (commercial/industrial), 240Δ.
Examples.
- “15 HP at 230 V, PF 0.9, 3-phase — what current?”
- “40 A at 120/208Y — what kW at PF 0.95?”
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3) Battery Runtime / Capacity Estimator
What it does. Estimates runtime (hours) or capacity needed for UPS / RV / vanlife / off-grid systems. Handles Wh↔Ah, stringing (series/parallel), inverter efficiency, and depth-of-discharge.
Inputs. Battery type (LiFePO₄ / Lead-acid), nominal voltage (12/24/48 V), capacity, load (W), inverter efficiency, usable DoD.
Example.
- 12 V 100 Ah LiFePO₄ ≈ 1,200 Wh; usable ~95% → ~1,140 Wh.
- A 60 W router + ONT → ~1,140 / 60 ≈ 19 h (idealized).
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4) Transformer kVA Calculators
What it does. Picks transformer kVA from load current/voltage (1-φ / 3-φ). Helps with step-up/step-down selections and common U.S. pairs (e.g., 480→208Y/120, 240/120).
Tips.
- Allow headroom for motor starting/inrush (often +25–50% depending on load type).
- Consider efficiency and PF when converting between kW/kVA.
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5) Energy / Cost Estimator
What it does. Estimates energy use (kWh) and monthly cost from duty cycle and local rate.
Defaults. U.S. blended rate examples: $0.12–$0.25/kWh (set your utility rate to be precise).
Note. Time-of-Use and tiered schedules vary by utility; this is a simple average cost model.
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FAQ about Calculators
Q1. Are these results “code-compliant”?
A: They’re planning estimates. Always verify conductor ampacity, adjustment, and correction with the NEC and your local AHJ. Field conditions (ambient, grouping, raceway fill, terminations) matter.
Q2. Can I switch between AWG and mm²?
A: Yes. We include an AWG↔mm² quick table and unit toggles where relevant.
Q3. Line-to-Line vs. Line-to-Neutral — which voltage do I use?
A: Depends on the load connection. 120/208Y and 277/480Y systems provide both L-L and L-N values. The converter helps you pick the right combination.
Q4. What PF should I use if I don’t know it?
A: For motors without correction, 0.85–0.90 is a reasonable starting point; resistive loads are ~1.0. Nameplates beat guesses.
Q5. Why 120/208Y and 277/480Y in the presets?
A: They’re the most common three-phase services in U.S. commercial/industrial buildings.
Downloads & Safety
- PDF: Voltage Drop & Feeder Cheat Sheet (U.S. presets)
- Mini-card: Verify-De-energize-Lockout (LOTO) checklist
- Reminder: Always test for absence of voltage with the right meter/NCVT before touching conductors.
I’m ready to calculate for Calculators
Voltage Drop Calculator｜Single- / Three-Phase Power Converter｜Battery Runtime / Capacity Estimator｜Transformer kVA Calculator｜Energy / Cost Estimator