As many of us know, it's possible to work out the current hammer count in a rival city's production box by looking at the cost shown in the espionage screen for the Sabotage Production mission. Here's the original post at Apolyton.
I just figured out a better way than that formula, so you don't have to go fishing around for the EP numbers on each side. The key is the Influence Civics mission and its constant base cost of 600 and the fact that the exact same multiplier applies to both it and Sabotage. The formula comes out this easy:
Hammers = SabotageCost / InfluenceCivicsCost * 100
And it's very easy to approximate in your head thanks to that 100 factor. (It appears because the base cost for Influence Civics is 600 and the cost for Sabotage is 6 * hammers.) When the sabotage cost equals the civics cost, the city has 100 hammers. Twice the civics cost means 200 hammers. Half the civics cost means 50 hammers, and so on.
Edit: Turns out that the cost for Influence Civics IS modified by game speed. So you need to include the game speed factor to get the hammer count.
Hammers = SabotageCost / InfluenceCivicsCost * 67 (quick speed)
Hammers = SabotageCost / InfluenceCivicsCost * 150 (epic speed)
Hammers = SabotageCost / InfluenceCivicsCost * 200 (marathon speed)
Also, if you are in exactly all the same civics as your target, there will be no value shown for Influence Civics. If you have a different religion than your target, you can use Influence Religion instead with all the same math. If your civics and religion both match your target, you can use the Support City Revolt mission as a baseline. This is the formula, which is not modified for game speed:
Hammers = SabotageCost / CityRevoltCost * 650 / 6
I just figured out a better way than that formula, so you don't have to go fishing around for the EP numbers on each side. The key is the Influence Civics mission and its constant base cost of 600 and the fact that the exact same multiplier applies to both it and Sabotage. The formula comes out this easy:
Hammers = SabotageCost / InfluenceCivicsCost * 100
And it's very easy to approximate in your head thanks to that 100 factor. (It appears because the base cost for Influence Civics is 600 and the cost for Sabotage is 6 * hammers.) When the sabotage cost equals the civics cost, the city has 100 hammers. Twice the civics cost means 200 hammers. Half the civics cost means 50 hammers, and so on.
Edit: Turns out that the cost for Influence Civics IS modified by game speed. So you need to include the game speed factor to get the hammer count.
Hammers = SabotageCost / InfluenceCivicsCost * 67 (quick speed)
Hammers = SabotageCost / InfluenceCivicsCost * 150 (epic speed)
Hammers = SabotageCost / InfluenceCivicsCost * 200 (marathon speed)
Also, if you are in exactly all the same civics as your target, there will be no value shown for Influence Civics. If you have a different religion than your target, you can use Influence Religion instead with all the same math. If your civics and religion both match your target, you can use the Support City Revolt mission as a baseline. This is the formula, which is not modified for game speed:
Hammers = SabotageCost / CityRevoltCost * 650 / 6