Start with a basic unit -- one liter, meter or gram.
Divide by 10 (10^-1 or 1/10 meter) for a decimeter, deciliter or decigram.
Divide the decimeter by 10 for a centimeter (10^-2 or 1/100 meter).
Divide a centimeter by another 10 for a millimeter (10^-3 or 1/1000 meter).
Divide a millimeter by another 1000 or 1 x 10^-3 for a micrometer (10^-6 or 1/1,000,000 meter).
Divide a micrometer by another 1,000 for a nanometer (10^-9 meter).
Multiply the positive exponent by 10^x, to convert from a positive prefix. "x" is the difference of the positive and negative exponent. For example, to convert a kilometer (1x10^3 meters) to a centimeter (1x10^-2 meters), subtract the positive exponent by the negative (3-(-2)=5) and multiply the positive exponent by 10^(value of the difference). When multiplying exponents, the values of the two exponents are added: 1x10^3 x 10^5 = 1x1-^(3+5) = 1x10^8, so one kilometer (1x10^3 meters) is equal to 1x10^8 cm.
Start with a basic unit -- one liter, meter, or gram.
Multiply by 10 (10^1 or 10 meters) for a dekameter.
Multiply a dekameter by 10 for a hectometer (10^2 or 100 meters).
Multiply a hectometer by 10 for a kilometer (10^3 or 1000 meters).
Multiply a kilometer by 1000 (10^3) for a megameter (10^6 or 1,000,000 meters).
Multiply a megameter by another 1000 for a gigameter (10^9 meters).
Multiply a gigameter by another 1000 for a terameter (10^12 meters).
Divide the positive exponent by 10^x to convert from a negative prefix. "x" is the difference of the positive and negative exponent. For example, to convert a centimeter (1x10^-2 meters) to a kilometer (1x10^3 meters), subtract the positive exponent by the negative (3-(-2)=5) and divide the negative exponent by 10^(value of the difference). When dividing exponents, the values of the two exponents are subtracted: 1x10^-2 / 10^5 = 1x10^(-2-5)=1x10^-7, so one centimeter (1x10^-2 meters) is equal to 1x10^-7 kilometers.