Example 1
Rz = 147 Ω.
Resistors in Series Calculator
Type R1 [Ω] and R2 [Ω]. The calculator computes Rz = R1+R2: 100 Ω and 47 Ω is 147 Ω, and two 10 Ω resistors are 20 Ω. In series the current is the same and voltage drops add.
Parallel: Rz = R1·R2/(R1+R2). Single R: R = U/I.
Result
Resistance R1 (Ω) and Resistance R2 (Ω). The result shows up here.
How it works
Series equivalent resistance is a sum: Rz = R1 + R2. At 100 Ω and 47 Ω you get 147 Ω. At two 10 Ω you get 20 Ω. At 1000 Ω and 2200 Ω you get 3200 Ω. In series the same I flows, and voltages add: U1 + U2 = Uz. Rz always grows.
The form has two fields: R1 and R2 in ohms. The result is in ohms. Type 2.2 kΩ as 2200, not as 2.2. A comma and a period mean the same R2: 47,5 and 47.5.
Typed 0 in one field makes Rz equal the other: zero ohms adds nothing. Both fields need a number before 147 Ω appears. A negative R in a homework line can be a sign; in this calculator you leave ohms positive.
In parallel 1/Rz = 1/R1 + 1/R2, so Rz is smaller than either resistor. Here a sum. R = U/I is one resistor from Ohm. This calculator already takes two R values.
Three resistors take two steps: first Rz from R1 and R2, then that Rz plus R3. The calculator has two fields. You can drop the finished Rz into U = I R or P = U I as one resistor.
Type 100 and 47, click Calculate, and check 147 Ω. Two 10 Ω resistors give 20 Ω. The calculator adds two numbers; it does not lay out a PCB.
How to use
- In the first field enter R1 in ohms, for example 100. 2.2 kΩ is 2200.
- In the second field enter R2 in ohms, for example 47.
- Click Calculate. The calculator adds R1 and R2. 100 and 47 give 147 Ω. Two 10 Ω resistors give 20 Ω.
- Typed 0 adds 0, so Rz equals the other. Both fields need a number.
- For parallel Rz, open resistors in parallel. One R from U and I is on R = U/I.
Formula
Rz = R1 + R2
Same current I through both resistors.
Rz, R1, and R2 in series
Series adds ohms: Rz = R1+R2. 100 Ω and 47 Ω is 147 Ω. The current through both is the same.
- Rz
- Series equivalent [Ω]. 10 Ω + 10 Ω = 20 Ω. Larger than each part.
- R1
- First resistance [Ω], for example 100. The drop on it is I·R1.
- R2
- Second resistance [Ω], for example 47 Ω. Added to R1 it gives Rz.
- I
- The same current [A] through R1 and R2. Voltages add, current does not.
Real-life examples
Example 2
Rz = 20 Ω.
Example 3
Rz = 3200 Ω.
Example 4
Rz = 5030 Ω.
Example 5
Rz = 44 Ω.
Example 6
Rz = 200 Ω.
Example 7
Rz = 2 Ω.
Example 8
Rz = 680 Ω.
Example 9
Series divider.
Example 10
Rz = 3.5 Ω.
Ways to use this calculator
- You add 100 Ω and 47 Ω to 147 Ω.
- You check two 10 Ω resistors: 20 Ω.
Frequently asked questions
How much Rz at 100 Ω and 47 Ω?
Equivalent resistance is 147 Ω. In series the ohms add: 100 + 47. That is not the parallel reciprocal.
How much with two 10 Ω?
You get 20 Ω. Two equal resistors in series double the resistance; they do not halve it.
Which units do I type?
Both resistances R1 [Ω] and R2 [Ω]. Result Rz [Ω].
How is this different from parallel?
Series adds: Rz = R1 + R2 and the result is larger. Parallel uses 1/Rz = 1/R1 + 1/R2 and Rz shrinks.
Does a comma in 47.5 work?
Yes. 47.5 and 47,5 are the same R [Ω]. A comma and a period mean the same value.
Is the current the same?
Yes. In series the same I [A] flows through both branches. Voltage drops U = I R add.
Where is R = U/I?
On the Ohm-law resistance page. There one R from measured U and I. Here you already add two R values.
What about three resistors?
This calculator has two fields. Add the third to Rz and run again, or combine two first, then the third.
What if one R is 0?
Rz equals the other branch. Zero ohms in series adds nothing. Both fields still need a number.
How much at 1000 Ω and 2200 Ω?
You get 3200 Ω. A thousand plus two thousand two hundred, a plain sum.
Knowledge sources
The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.
Page updated in 2026.