In our preparation for the office move we did some calculation of the load(wattage) required by Cisco Switches, servers, routers and other IT equipment so as to understand the average KW required in the new office.
A 2950, 2960G, 3550. A 2811, 2821, 3700 -
all the above running in full steam required 60-70 W. each
so you can take this figure (70 as an upper value) and multiple it with the number of devices u have.
You probably will not need maximum faceplate power for a lab. Any router that is not loaded up with VPN feature cards and does not have all slots populated will burn much less power automatically.
Any router that is not processing volumes of traffic will have its internal fans run cooler/slower and burn much less power. The same for switches.
You may be albe to get all the above on a 20A circuit breaker but 2 circuits would be better. You may pull operationally 16Amps. If it pulls more you must split it.
You can also run Cisco Gear at 240 Volt (like a home stove or window AC) and it may run 20% more efficent and a circuit would run everything.
New generation (last 36 mo.) will burn less power than the older generation gear.
The faceplate/NAMEPLATE power varies from generation to generation of gear too, and the nameplate power is when the gear is maxed out.
Software Power calculator will probably overestimate what you need.
Wattage is good to know if you want to look for UPS load calculation.
Amperage, however, is your actual USAGE that would translate to billing or to overloading/tripping a circuit.
There are some surge bars you can buy that have build in amp (and watt/volt) level LCD in them, which may be helpful to you!
I have a power monitor that gives me a rough update on my current power usage. I plugged in my rack and powered it all on and although it initially spiked I reckon the usage on it was between 1 and 1.5 Kilo Watts per hour.
You can calculate the maximum usage on your devices by looking at the labels on them. So if you take the AMPs and multiple them by the Voltage you should get the Watts. You then take this figure and figure out how many Watts you would use an hour. You are usually billed on the Watts or KiloWatts you use an hour.
The other thing you will have to worry about is triping the circuit in your house so that depends on what the circuit is rated for. In most countries where the UK was involved your ring main will probably be rated for 30 amps so that should be more than enough. However if you will probably want to spread the load across a couple of plugs sockets and not turn all your equipment on at the same time if you are in a country that uses AC/DC power.
Overall the power bill for your home rack will not be to high. Electronic equipment generally does not draw that much power despite the green hysteria that goes arround the things that cost you money are anything that heats something.