Electronics calculator
Ohm's law, voltage divider, LED resistor, colour and SMD codes, battery life and S×P packs, RC circuits and wire voltage drop. Results and schematics update as you type; values are picked from the standard series.
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Ohm's law and power
Enter any two values and the other two are calculated. Prefixes: 4k7, 330m, 2.2M, 10u.
= 2.553 mA
= 4.7 kΩ
= 30.64 mW
- given
- calculated
- formula used
I = V/R = 2.553 mA
P = V²/R = 30.64 mW
How it works
Type it like a schematic
Fields understand SI prefixes and RKM notation: 4k7, 2.2M, 330m, 10u, 1R5, plus units such as “20 mA”. Under each field you see how the value was read.
Instant results
There is no “Calculate” button: results, formulas with substituted values and the schematic redraw on every change. The divider sliders step only through standard values of the chosen series.
Standard values
The divider finds the best E6–E96 pair with the same total resistance (so the divider current stays the same), the LED resistor rounds up to the nearest standard value, and the colour code tells you whether a value is in a series.
Report and versions
A Markdown or PDF report collects the results of every tab; JSON keeps the fields and loads back; versions help compare circuit options.
Formulas and standards
The tables below are generated from the same code as the calculation. E series follow IEC 60063:2015, the colour code IEC 60062:2016 (which added the pink ×0.001 multiplier), AWG gauges ASTM B258 and metric sizes IEC 60228.
Ohm's law and power
- Formula
- V = I·R; P = V·I = I²·R = V²/R
Voltage divider
- Formula
- Vout = Vin · R2′ / (R1 + R2′), R2′ = R2 ∥ RL = R2·RL / (R2 + RL)
R2 for a target Vout
- Formula
- R2′ = R1 · Vout / (Vin − Vout); R2 = R2′·RL / (RL − R2′)
LED resistor
- Formula
- R = (Vs − n·Vf) / I; P = I²·R; power rating ≥ P × margin
Profile average current
- Formula
- Iavg = (Ia·ta + Is·ts) / (ta + ts)
Runtime
- Formula
- t = C·Vbat·DoD·(1 − ktemp)·(1 − kage) / (Vload·Iavg/η + Pself)
S×P pack
- Formula
- V = S·Vcell; C = P·Ccell; E = S·P·V·C
RC circuit
- Formula
- τ = R·C; fc = 1/(2π·R·C); V(t) = V·(1 − e^(−t/τ)); E = ½·C·V²
Wire
- Formula
- d = 0.127·92^((36 − AWG)/39) mm; R = ρ·(1 + α·(T − 20))·2L/S; ΔU = I·R
E6
- Tolerance
- ±20 %
- Values
- 1 · 1.5 · 2.2 · 3.3 · 4.7 · 6.8
E12
- Tolerance
- ±10 %
- Values
- 1 · 1.2 · 1.5 · 1.8 · 2.2 · 2.7 · 3.3 · 3.9 · 4.7 · 5.6 · 6.8 · 8.2
E24
- Tolerance
- ±5 %
- Values
- 1 · 1.1 · 1.2 · 1.3 · 1.5 · 1.6 · 1.8 · 2 · 2.2 · 2.4 · 2.7 · 3 · 3.3 · 3.6 · 3.9 · 4.3 · 4.7 · 5.1 · 5.6 · 6.2 · 6.8 · 7.5 · 8.2 · 9.1
E48
- Tolerance
- ±2 %
- Values
- 48 three-digit values — every second E96 value
E96
- Tolerance
- ±1 %
- Values
- 1 · 1.02 · 1.05 · 1.07 · 1.1 · 1.13 · 1.15 · 1.18 · 1.21 · 1.24 · 1.27 · 1.3 · 1.33 · 1.37 · 1.4 · 1.43 · 1.47 · 1.5 · 1.54 · 1.58 · 1.62 · 1.65 · 1.69 · 1.74 · 1.78 · 1.82 · 1.87 · 1.91 · 1.96 · 2 · 2.05 · 2.1 · 2.15 · 2.21 · 2.26 · 2.32 · 2.37 · 2.43 · 2.49 · 2.55 · 2.61 · 2.67 · 2.74 · 2.8 · 2.87 · 2.94 · 3.01 · 3.09 · 3.16 · 3.24 · 3.32 · 3.4 · 3.48 · 3.57 · 3.65 · 3.74 · 3.83 · 3.92 · 4.02 · 4.12 · 4.22 · 4.32 · 4.42 · 4.53 · 4.64 · 4.75 · 4.87 · 4.99 · 5.11 · 5.23 · 5.36 · 5.49 · 5.62 · 5.76 · 5.9 · 6.04 · 6.19 · 6.34 · 6.49 · 6.65 · 6.81 · 6.98 · 7.15 · 7.32 · 7.5 · 7.68 · 7.87 · 8.06 · 8.25 · 8.45 · 8.66 · 8.87 · 9.09 · 9.31 · 9.53 · 9.76
black
- Digit
- 0
- Multiplier
- ×1
- Tolerance
- —
- Tempco, ppm/K
- 250
brown
- Digit
- 1
- Multiplier
- ×10
- Tolerance
- ±1 % (F)
- Tempco, ppm/K
- 100
red
- Digit
- 2
- Multiplier
- ×100
- Tolerance
- ±2 % (G)
- Tempco, ppm/K
- 50
orange
- Digit
- 3
- Multiplier
- ×1k
- Tolerance
- ±0.05 % (W)
- Tempco, ppm/K
- 15
yellow
- Digit
- 4
- Multiplier
- ×10k
- Tolerance
- ±0.02 % (P)
- Tempco, ppm/K
- 25
green
- Digit
- 5
- Multiplier
- ×100k
- Tolerance
- ±0.5 % (D)
- Tempco, ppm/K
- 20
blue
- Digit
- 6
- Multiplier
- ×1M
- Tolerance
- ±0.25 % (C)
- Tempco, ppm/K
- 10
violet
- Digit
- 7
- Multiplier
- ×10M
- Tolerance
- ±0.1 % (B)
- Tempco, ppm/K
- 5
grey
- Digit
- 8
- Multiplier
- ×100M
- Tolerance
- ±0.01 % (L)
- Tempco, ppm/K
- 1
white
- Digit
- 9
- Multiplier
- ×1G
- Tolerance
- —
- Tempco, ppm/K
- —
gold
- Digit
- —
- Multiplier
- ×100m
- Tolerance
- ±5 % (J)
- Tempco, ppm/K
- —
silver
- Digit
- —
- Multiplier
- ×10m
- Tolerance
- ±10 % (K)
- Tempco, ppm/K
- —
pink
- Digit
- —
- Multiplier
- ×1m
- Tolerance
- —
- Tempco, ppm/K
- —
no band
- Digit
- —
- Multiplier
- —
- Tolerance
- ±20 % (M)
- Tempco, ppm/K
- —
Limitations
- The formulas are ideal: component tolerance and drift, source resistance and parasitic capacitance or inductance are not included.
- An LED's forward voltage depends on current, temperature and batch. The colour presets are typical ranges; use the datasheet value.
- Battery runtime is a linear model: it ignores capacity loss at high discharge current (Peukert's law), voltage cut-off under load and current spikes. For an exact answer, measure the current profile.
- The wire calculation gives the voltage drop, not the ampacity: allowed current depends on insulation and installation (IEC 60364-5-52, NEC 310).
- The divider pair search keeps the total resistance within half a decade of the current one; to change the divider current, change R1 and R2 first.
Privacy
- All calculations run in your browser: calculating never sends the values you enter to a server or puts them in the page address.
- Fields and versions are kept in this browser's localStorage; “Reset” restores the defaults, and versions are deleted one by one.
- Analytics receives only the fact of loading the example or exporting and the file format — no values.
- The result reaches us only if you send a request yourself and keep the “Attach the result” box ticked — the form shows exactly what will be sent: the open tab, its inputs and the result with units.
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