Formula Lab
Every result shows its work, exam-paper style. Change any input and the steps recompute instantly.
Solver 01
Ohm's Law + Power
Enter exactly two of V, I, R — the solver derives the third and chains into power.
I = V / R
I = 120 V / 15 Ω
I = 8 A
P = V × I
P = 120 × 8
→ I = 8 A · P = 960 W
Solver 02
Voltage Drop (single-phase)
VD = 2 × K × I × L ÷ CM. Rule of thumb: keep branch-circuit drop at or under 3%.
VD = 2 × K × I × L / CM
VD = 2 × 12.9 × 16 A × 85 ft / 6,530 cmil
VD = 5.37 V
% drop = VD / V_source × 100
% drop = 5.37 / 120 × 100
→ 5.37 V drop · 4.48% ✗ exceeds 3% — upsize the conductor
Single-phase, two-wire formula with DC-resistance K values — the standard exam approximation. Real designs also account for power factor and conductor temperature.
Solver 03
Series / Parallel Resistance
Any number of resistors; parallel results are always below the smallest branch.
1/R_T = 1/R₁ + 1/R₂ + …
1/R_T = 1/10 + 1/20 + 1/30
1/R_T = 0.183
R_T = 1 ÷ 0.183
→ R_T = 5.455 Ω (always below the smallest branch: 10 Ω)
Solver 04
Conduit Offset Bends
Distance between marks and shrink, from the memorized multiplier table (Cert 3, Unit 3.2).
Distance between bends = depth × multiplier
Distance = 4 in × 2 (30° multiplier)
Distance = 8 in
Shrink = depth × shrink constant
Shrink = 4 × 0.25 in/in
→ 8 in between marks · 1 in shrink — add it to your measurement before marking
Shallower angles pull easier; steeper angles save space. Total bends between pull points may not exceed 360°.