Media Buying Interview Prep & Cheat Sheet

The formulas, terms, and benchmarks you need for your media buying interview — or your first week at the agency. Bookmark this page or print it out.

Must-Know Formulas

CPM

CPM = (Budget ÷ Impressions) × 1,000

Cost of 1,000 impressions. The universal unit of media pricing.

CPC

CPC = Spend ÷ Clicks

Cost per click. Standard for search and paid social.

CPA

CPA = Spend ÷ Conversions

Cost per conversion. The performance marketer's north star.

CTR

CTR = (Clicks ÷ Impressions) × 100

Click-through rate. Measures creative effectiveness.

ROAS

ROAS = Revenue ÷ Spend

Revenue per dollar spent. Not profit — that's ROI.

ROI

ROI = (Revenue − Cost) ÷ Cost × 100

Profit as a percentage of cost. 100% = doubled your money.

Reach & Frequency

Impressions = Reach × Frequency

Width × depth. Aim for 3–7 freq for awareness.

GRP

GRP = Reach % × Frequency

TV media weight. TRP = same formula for target audience.

CPP

CPP = Cost ÷ GRP

Cost of one rating point. TV's equivalent of CPM.

Gross / Net

Gross = Net ÷ (1 − Commission%)

Commission is % of gross, not net. Standard: 15%.

Margin

Margin = (Revenue − Cost) ÷ Revenue × 100

Profit as % of revenue. Don't confuse with markup.

% Change

% Change = (Current − Previous) ÷ Previous × 100

Reporting staple. Always include direction + absolute values.

Key Terms to Know

Impression: A single render of an ad to a user's screen.
Reach: The number of unique people who saw the ad at least once.
Frequency: Average number of times each person saw the ad.
Flight: The start and end dates of a campaign or buy.
Daypart: A time block (morning, daytime, prime, late night) used in TV/radio buying.
Insertion Order (IO): A signed agreement between buyer and seller specifying the terms of a media buy.
RFP: Request for Proposal — sent to media vendors asking for inventory, rates, and recommendations.
DSP: Demand-Side Platform — the tool buyers use to bid on and purchase programmatic inventory.
SSP: Supply-Side Platform — the tool publishers use to sell their inventory programmatically.
Working Media: The dollars that actually buy ad inventory, after fees and commissions.
Non-Working Media: Production, tech fees, agency fees, and other costs that don't buy impressions.
Make-Good: Free inventory or credit a publisher provides when original delivery fell short.
Added Value: Bonus impressions, sponsorships, or placements thrown in beyond the paid buy.
Viewability: The percentage of impressions that met the MRC standard (50% of pixels in view for 1 second, 2 seconds for video).
Brand Safety: Ensuring ads don't appear alongside harmful, offensive, or off-brand content.

Quick Benchmarks

Metric	Typical Range	Notes
Display CPM	$2 – $8	Standard banners; varies by targeting
Video CPM	$15 – $30	Pre-roll; CTV can be $25–$50+
Social CPC	$0.50 – $3.00	Meta, LinkedIn, X (varies widely)
Search CPC	$1 – $5+	Highly dependent on vertical/keywords
Display CTR	0.05% – 0.10%	Standard banners
Search CTR	2% – 5%	Top positions; brand terms higher
Agency commission	10% – 15%	Of gross; varies by contract
Tech fee overhead	25% – 40%	Programmatic total (DSP + data + verification)

Benchmarks are approximate and vary by industry, geography, and time of year. Use them as conversation starters, not guarantees.

Test Yourself

Try solving these before checking the answer. They're the kind of quick-math questions that come up in interviews and on the job.

1.A client has a $200,000 budget and expects a $15 CPM. How many impressions can they buy?

(200,000 ÷ 15) × 1,000 = 13,333,333 impressions.

2.A campaign spent $50,000 and drove 2,500 conversions. What's the CPA?

50,000 ÷ 2,500 = $20 CPA.

3.ROAS is 5×. The product margin is 30%. Is the campaign profitable?

Yes. 5× ROAS means $5 revenue per $1 spent. 30% margin on $5 = $1.50 profit per $1 spent = 50% ROI.

4.CPC went from $1.80 to $2.16. What's the percent change?

(2.16 − 1.80) ÷ 1.80 × 100 = +20% increase.

5.A TV buy delivered 75% reach at 4× frequency. How many GRPs?

75 × 4 = 300 GRPs.

6.Net media cost is $170,000. Agency commission is 15% of gross. What's the gross?

170,000 ÷ (1 − 0.15) = 170,000 ÷ 0.85 = $200,000 gross.

7.A programmatic buy has a $10 CPM, 12% DSP fee, 5% data fee, and $0.10 CPM verification. What's the effective CPM?

Media: $10 + DSP: $1.20 + Data: $0.50 + Verification: $0.10 = $11.80 effective CPM.

8.Total budget is $60,000 over 30 days. After 12 days you've spent $28,000. Are you ahead or behind pace?

Even pace at day 12 = $60,000 × (12/30) = $24,000. You've spent $28,000 — ahead of pace by $4,000. Slow down.

Keep going

Read the full Media Math 101 guide, explore the common planner questions, or try any of the free calculators.